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(<!-- -->1.3.0<!-- -->).</div></div><div class=docItemContainer_Djhp><article><nav class="theme-doc-breadcrumbs breadcrumbsContainer_Z_bl" aria-label=Breadcrumbs><ul class=breadcrumbs><li class=breadcrumbs__item><a aria-label="Home page" class=breadcrumbs__link href=/><svg viewBox="0 0 24 24" class=breadcrumbHomeIcon_YNFT><path d="M10 19v-5h4v5c0 .55.45 1 1 1h3c.55 0 1-.45 1-1v-7h1.7c.46 0 .68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill=currentColor /></svg></a><li class="breadcrumbs__item breadcrumbs__item--active"><span class=breadcrumbs__link>Xlang Implementation Guide</span></ul></nav><span class="theme-doc-version-badge badge badge--secondary">Version: 1.2.0</span><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type=button class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><header><h1>Xlang Implementation Guide</h1></header><h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=overview>Overview<a href=#overview class=hash-link aria-label="Direct link to Overview" title="Direct link to Overview" translate=no></a></h2> |
| <p>This guide describes the current xlang implementation ownership model used by |
| the reference Java implementation and mirrored by the Dart implementation rewrite.</p> |
| <p>The wire format is defined by |
| <a class="" href=/docs/1.2.0/specification/xlang_serialization_spec>Xlang Serialization Spec</a>. This document is about |
| service boundaries, operation flow, and internal ownership. New language implementations do not |
| need the same class names, but they should preserve the same control flow:</p> |
| <ul> |
| <li class="">root operations stay on the <code>Fory</code> facade</li> |
| <li class="">nested payload work stays on explicit read and write contexts</li> |
| <li class="">type metadata stays in the type resolver layer</li> |
| <li class="">serializers stay payload-focused</li> |
| </ul> |
| <p>When this guide conflicts with the wire-format specification, follow |
| <code>docs/specification/xlang_serialization_spec.md</code>. When it conflicts with a |
| language-specific implementation detail, follow the current implementation code for |
| that language.</p> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=source-of-truth>Source Of Truth<a href=#source-of-truth class=hash-link aria-label="Direct link to Source Of Truth" title="Direct link to Source Of Truth" translate=no></a></h2> |
| <p>Use these sources in this order:</p> |
| <ol> |
| <li class=""><code>docs/specification/xlang_serialization_spec.md</code></li> |
| <li class="">the current implementation for the language</li> |
| <li class="">cross-language tests under <code>integration_tests/</code></li> |
| </ol> |
| <p>For Dart, the implementation shape is centered on:</p> |
| <ul> |
| <li class=""><code>Fory</code></li> |
| <li class=""><code>WriteContext</code></li> |
| <li class=""><code>ReadContext</code></li> |
| <li class=""><code>RefWriter</code></li> |
| <li class=""><code>RefReader</code></li> |
| <li class=""><code>TypeResolver</code></li> |
| <li class=""><code>StructSerializer</code></li> |
| </ul> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=implementation-ownership-model>Implementation Ownership Model<a href=#implementation-ownership-model class=hash-link aria-label="Direct link to Implementation Ownership Model" title="Direct link to Implementation Ownership Model" translate=no></a></h2> |
| <h3 class="anchor anchorTargetStickyNavbar_Vzrq" id=fory-is-the-root-operation-facade><code>Fory</code> is the root-operation facade<a href=#fory-is-the-root-operation-facade class=hash-link aria-label="Direct link to fory-is-the-root-operation-facade" title="Direct link to fory-is-the-root-operation-facade" translate=no></a></h3> |
| <p><code>Fory</code> owns the reusable services for one Fory instance.</p> |
| <p>In Dart, <code>Fory</code> owns exactly four reusable members:</p> |
| <ul> |
| <li class=""><code>Buffer</code></li> |
| <li class=""><code>WriteContext</code></li> |
| <li class=""><code>ReadContext</code></li> |
| <li class=""><code>TypeResolver</code></li> |
| </ul> |
| <p>In Java, <code>Fory</code> also owns instance-local services such as <code>JITContext</code> and |
| <code>CopyContext</code>, but the ownership rule is the same: <code>Fory</code> is the root facade, |
| not the place where nested serializers do their work.</p> |
| <p><code>Fory</code> is responsible for:</p> |
| <ul> |
| <li class="">preparing the shared buffer for root operations</li> |
| <li class="">writing and reading the root xlang header bitmap</li> |
| <li class="">delegating nested value encoding to <code>WriteContext</code></li> |
| <li class="">delegating nested value decoding to <code>ReadContext</code></li> |
| <li class="">owning registration through <code>TypeResolver</code></li> |
| <li class="">resetting operation-local context state in a top-level <code>finally</code></li> |
| </ul> |
| <p>Nested serializers must not call back into root <code>serialize(...)</code> or |
| <code>deserialize(...)</code> entry points.</p> |
| <h3 class="anchor anchorTargetStickyNavbar_Vzrq" id=writecontext-and-readcontext-hold-operation-local-state><code>WriteContext</code> and <code>ReadContext</code> hold operation-local state<a href=#writecontext-and-readcontext-hold-operation-local-state class=hash-link aria-label="Direct link to writecontext-and-readcontext-hold-operation-local-state" title="Direct link to writecontext-and-readcontext-hold-operation-local-state" translate=no></a></h3> |
| <p><code>WriteContext</code> and <code>ReadContext</code> are prepared by <code>Fory</code> for one root operation |
| and reset by <code>Fory</code> in a <code>finally</code> block before reuse.</p> |
| <p><code>prepare(...)</code> should only bind the active buffer and root-operation inputs. |
| <code>reset()</code> should clear operation-local mutable state.</p> |
| <p>That operation-local state includes:</p> |
| <ul> |
| <li class="">the current buffer</li> |
| <li class="">the active <code>RefWriter</code> or <code>RefReader</code></li> |
| <li class="">meta-string state</li> |
| <li class="">shared type-definition state</li> |
| <li class="">operation-local scratch state keyed by identity</li> |
| <li class="">logical object-graph depth</li> |
| </ul> |
| <p>Generated and hand-written serializers should treat these contexts as the only |
| source of operation-local services. Serializers must not keep ambient instance |
| state in thread locals, globals, or serializer instance fields.</p> |
| <h3 class="anchor anchorTargetStickyNavbar_Vzrq" id=writecontext><code>WriteContext</code><a href=#writecontext class=hash-link aria-label="Direct link to writecontext" title="Direct link to writecontext" translate=no></a></h3> |
| <p><code>WriteContext</code> owns all write-side per-operation state:</p> |
| <ul> |
| <li class="">current <code>Buffer</code></li> |
| <li class=""><code>RefWriter</code></li> |
| <li class=""><code>MetaStringWriter</code></li> |
| <li class="">shared TypeDef write state</li> |
| <li class="">root <code>trackRef</code> mode</li> |
| <li class="">recursion depth and limits</li> |
| </ul> |
| <p>It exposes one-shot primitive helpers such as:</p> |
| <ul> |
| <li class=""><code>writeBool</code></li> |
| <li class=""><code>writeInt32</code></li> |
| <li class=""><code>writeVarUInt32</code></li> |
| </ul> |
| <p>These helpers are convenience methods. Serializers that perform repeated |
| primitive IO should cache <code>final buffer = context.buffer;</code> and call buffer |
| methods directly.</p> |
| <h3 class="anchor anchorTargetStickyNavbar_Vzrq" id=readcontext><code>ReadContext</code><a href=#readcontext class=hash-link aria-label="Direct link to readcontext" title="Direct link to readcontext" translate=no></a></h3> |
| <p><code>ReadContext</code> owns all read-side per-operation state:</p> |
| <ul> |
| <li class="">current <code>Buffer</code></li> |
| <li class=""><code>RefReader</code></li> |
| <li class=""><code>MetaStringReader</code></li> |
| <li class="">shared TypeDef read state</li> |
| <li class="">recursion depth and limits</li> |
| </ul> |
| <p>It exposes matching one-shot primitive helpers such as:</p> |
| <ul> |
| <li class=""><code>readBool</code></li> |
| <li class=""><code>readInt32</code></li> |
| <li class=""><code>readVarUInt32</code></li> |
| </ul> |
| <p>Generated struct serializers call <code>context.reference(value)</code> immediately after |
| constructing the target instance so back-references can resolve to that object.</p> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=reference-tracking>Reference Tracking<a href=#reference-tracking class=hash-link aria-label="Direct link to Reference Tracking" title="Direct link to Reference Tracking" translate=no></a></h2> |
| <p>Reference handling is split behind two explicit services:</p> |
| <ul> |
| <li class=""><code>RefWriter</code> writes null, ref, and new-value markers and remembers previously |
| written objects by identity.</li> |
| <li class=""><code>RefReader</code> decodes those markers, reserves read reference IDs, and resolves |
| previously materialized objects.</li> |
| </ul> |
| <p>The xlang ref markers are:</p> |
| <ul> |
| <li class=""><code>NULL_FLAG (-3)</code></li> |
| <li class=""><code>REF_FLAG (-2)</code></li> |
| <li class=""><code>NOT_NULL_VALUE_FLAG (-1)</code></li> |
| <li class=""><code>REF_VALUE_FLAG (0)</code></li> |
| </ul> |
| <p>Key behavior:</p> |
| <ul> |
| <li class="">basic values never use ref tracking</li> |
| <li class="">field metadata controls ref behavior inside generated structs</li> |
| <li class="">root <code>trackRef</code> is only for top-level graphs and container roots with no |
| field metadata</li> |
| <li class="">serializers that allocate an object before all nested reads complete must bind |
| that object early with <code>context.reference(...)</code></li> |
| </ul> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=type-resolution>Type Resolution<a href=#type-resolution class=hash-link aria-label="Direct link to Type Resolution" title="Direct link to Type Resolution" translate=no></a></h2> |
| <p><code>TypeResolver</code> owns:</p> |
| <ul> |
| <li class="">built-in type resolution</li> |
| <li class="">registration by numeric id or by <code>namespace + typeName</code></li> |
| <li class="">serializer lookup</li> |
| <li class="">struct metadata lookup</li> |
| <li class="">type metadata encoding and decoding</li> |
| <li class="">canonical encoded meta strings for package names, type names, and field names</li> |
| <li class="">encoded-name lookup for named type resolution</li> |
| <li class="">wire type decisions for struct, compatible struct, enum, ext, and union forms</li> |
| </ul> |
| <p>In Java xlang mode the concrete implementation is <code>XtypeResolver</code>. In Dart the |
| same ownership stays behind the internal <code>TypeResolver</code>.</p> |
| <p>Serializers do not resolve class metadata themselves. They ask the current |
| context to read or write nested values, and the context delegates type work to |
| <code>TypeResolver</code>.</p> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=root-frame-responsibilities>Root Frame Responsibilities<a href=#root-frame-responsibilities class=hash-link aria-label="Direct link to Root Frame Responsibilities" title="Direct link to Root Frame Responsibilities" translate=no></a></h2> |
| <p>Every root payload starts with a one-byte bitmap written and read by <code>Fory</code> |
| itself, not by serializers.</p> |
| <p>Current xlang root bits:</p> |
| <table><thead><tr><th>Bit<th>Meaning<tbody><tr><td><code>0</code><td>null root payload<tr><td><code>1</code><td>xlang payload<tr><td><code>2</code><td>out-of-band buffers in use</table> |
| <p>Keep the root bitmap separate from per-object ref markers:</p> |
| <ul> |
| <li class="">the root bitmap describes the whole payload</li> |
| <li class="">ref flags describe one nested value at a time</li> |
| </ul> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=serialization-flow>Serialization Flow<a href=#serialization-flow class=hash-link aria-label="Direct link to Serialization Flow" title="Direct link to Serialization Flow" translate=no></a></h2> |
| <h3 class="anchor anchorTargetStickyNavbar_Vzrq" id=root-write-path>Root write path<a href=#root-write-path class=hash-link aria-label="Direct link to Root write path" title="Direct link to Root write path" translate=no></a></h3> |
| <p>The current root write flow is:</p> |
| <ol> |
| <li class=""><code>Fory.serialize(...)</code> or <code>serializeTo(...)</code> prepares the target buffer.</li> |
| <li class=""><code>Fory</code> calls <code>writeContext.prepare(...)</code>.</li> |
| <li class=""><code>Fory</code> writes the root bitmap.</li> |
| <li class=""><code>Fory</code> delegates the root object to <code>WriteContext</code>.</li> |
| <li class=""><code>writeContext.reset()</code> runs in <code>finally</code>.</li> |
| </ol> |
| <p>For a non-null root value, <code>WriteContext.writeRootValue(...)</code> performs:</p> |
| <ol> |
| <li class="">ref/null framing</li> |
| <li class="">type metadata write</li> |
| <li class="">payload write</li> |
| </ol> |
| <p>Payload serializers are responsible only for the payload of their type. They do |
| not write the root bitmap and they do not own registration or type-header |
| encoding.</p> |
| <h3 class="anchor anchorTargetStickyNavbar_Vzrq" id=nested-writes-use-writecontext>Nested writes use <code>WriteContext</code><a href=#nested-writes-use-writecontext class=hash-link aria-label="Direct link to nested-writes-use-writecontext" title="Direct link to nested-writes-use-writecontext" translate=no></a></h3> |
| <p>Important rules:</p> |
| <ul> |
| <li class="">nested serializers must use <code>WriteContext</code> helpers such as <code>writeRef(...)</code>, |
| <code>writeNonRef(...)</code>, and container helpers when they need ref handling or type |
| metadata</li> |
| <li class="">repeated primitive writes should go directly through the buffer</li> |
| <li class="">nested serializer flow should stay straight-line; do not add internal |
| <code>try/finally</code> blocks just to clean per-operation state</li> |
| <li class="">top-level <code>Fory.serialize(...)</code> owns the operation reset <code>finally</code></li> |
| </ul> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=deserialization-flow>Deserialization Flow<a href=#deserialization-flow class=hash-link aria-label="Direct link to Deserialization Flow" title="Direct link to Deserialization Flow" translate=no></a></h2> |
| <h3 class="anchor anchorTargetStickyNavbar_Vzrq" id=root-read-path>Root read path<a href=#root-read-path class=hash-link aria-label="Direct link to Root read path" title="Direct link to Root read path" translate=no></a></h3> |
| <p>The current root read flow mirrors the write flow:</p> |
| <ol> |
| <li class=""><code>Fory.deserialize(...)</code> or <code>deserializeFrom(...)</code> reads the root bitmap.</li> |
| <li class="">null roots return immediately.</li> |
| <li class=""><code>Fory</code> validates xlang mode and other root framing requirements.</li> |
| <li class=""><code>Fory</code> calls <code>readContext.prepare(...)</code>.</li> |
| <li class=""><code>Fory</code> delegates to <code>ReadContext</code>.</li> |
| <li class=""><code>readContext.reset()</code> runs in <code>finally</code>.</li> |
| </ol> |
| <h3 class="anchor anchorTargetStickyNavbar_Vzrq" id=readcontext-owns-ref-reservation-and-payload-materialization><code>ReadContext</code> owns ref reservation and payload materialization<a href=#readcontext-owns-ref-reservation-and-payload-materialization class=hash-link aria-label="Direct link to readcontext-owns-ref-reservation-and-payload-materialization" title="Direct link to readcontext-owns-ref-reservation-and-payload-materialization" translate=no></a></h3> |
| <p><code>ReadContext.readRef()</code> performs the normal xlang read sequence:</p> |
| <ol> |
| <li class="">consume the next ref marker</li> |
| <li class="">return <code>null</code> or a back-reference immediately when appropriate</li> |
| <li class="">reserve a fresh read ref id for new reference-tracked values</li> |
| <li class="">read type metadata</li> |
| <li class="">read the payload</li> |
| <li class="">bind the reserved read ref id to the completed object</li> |
| </ol> |
| <p>Primitive and string-like hot paths should read directly from the buffer; |
| complex payloads delegate to the resolved serializer.</p> |
| <h3 class="anchor anchorTargetStickyNavbar_Vzrq" id=stream-and-buffer-byte-reads>Stream And Buffer Byte Reads<a href=#stream-and-buffer-byte-reads class=hash-link aria-label="Direct link to Stream And Buffer Byte Reads" title="Direct link to Stream And Buffer Byte Reads" translate=no></a></h3> |
| <p>Implementations must keep byte availability in the byte owner layer while |
| keeping string, binary, primitive-array, compression, and collection semantics in |
| serializers.</p> |
| <p>The required byte-owner primitive for allocation-before-read checks is a |
| readability check such as <code>checkReadableBytes(byteCount)</code>. Implementations do |
| not need additional generic read-context methods for this design. After the |
| readability check succeeds, serializers use their existing local buffer read, |
| copy, or decode paths.</p> |
| <p>The readability check is a byte operation only. It must not decode strings, |
| primitive-array element counts, compression modes, or collection capacity |
| policy.</p> |
| <p>For large byte-counted values, every implementation should call the byte-owner |
| readability check before allocating a variable-length result. This applies to |
| binary values, strings, decimal or metadata bodies, and primitive wire arrays |
| whose encoded body is measured in bytes. For multi-byte primitive wire arrays, |
| compare the encoded byte count, not only the logical element count, with the |
| readable bytes.</p> |
| <ol> |
| <li class="">Validate the encoded byte count in the serializer. For fixed-width primitive |
| arrays, check overflow and element alignment before allocation, such as |
| <code>wireByteCount % elementByteWidth == 0</code>, then derive the logical element |
| count from the encoded byte count.</li> |
| <li class="">Call <code>checkReadableBytes(wireByteCount)</code> unconditionally before allocating |
| the variable-length result. Buffer-backed inputs normally return from this |
| check with only a bounds comparison. Stream-backed inputs use the same call; |
| the byte owner handles the fast path when enough bytes are already buffered |
| and otherwise fills the read buffer until the requested encoded body is |
| readable or an input error is recorded.</li> |
| <li class="">After readability is proven, allocate the final value once and copy or decode |
| from the current readable buffer into the final result.</li> |
| </ol> |
| <p><code>checkReadableBytes</code> is not an <code>ensureCapacity(wireByteCount)</code> operation. In |
| stream mode it may end with the byte owner holding the full encoded body in its |
| read buffer, but it must grow that buffer as bytes are successfully read from |
| the stream. It should grow from current proven buffer capacity, such as by |
| doubling current capacity, and cap only when that bounded growth step reaches |
| the immediate target. A byte owner may use an owner-local availability signal as |
| a one-shot growth hint when the stream implementation itself is caller-owned |
| trusted code; if that hint is absent or insufficient, it must fall back to |
| bounded growth from already buffered bytes. It must not reserve the |
| attacker-declared length before input bytes or an owner-local growth hint |
| justify that intermediate buffer capacity. The stream slow path may pay one |
| extra intermediate buffer copy; this is preferable to serializer-local chunk |
| accumulation and repeated final-container growth.</p> |
| <p>For byte-counted values, the serializer should not duplicate the byte owner's |
| fast-path branch by testing <code>availableBytes()</code> before calling |
| <code>checkReadableBytes</code>. Keeping that branch in the byte owner gives every language |
| the same correctness rule and keeps serializer hot paths focused on their own |
| wire semantics.</p> |
| <p>For primitive wire arrays:</p> |
| <ul> |
| <li class="">Compare and prove the encoded wire byte count, not only the logical element |
| count.</li> |
| <li class="">Keep compression, bit-packing, byte-order conversion, and other primitive |
| array encoding semantics in the serializer. <code>checkReadableBytes</code> only proves |
| that the encoded bytes are present.</li> |
| <li class="">For compressed or transformed bodies, the serializer must still validate the |
| decoded length and encoding-specific metadata before allocating or returning |
| the final value.</li> |
| </ul> |
| <p>The common serializer shape is:</p> |
| <div class="language-text codeBlockContainer_Ckt0 theme-code-block" style=--prism-color:#393A34;--prism-background-color:#f6f8fa><div class=codeBlockContent_QJqH><pre tabindex=0 class="prism-code language-text codeBlock_bY9V thin-scrollbar" style=color:#393A34;background-color:#f6f8fa><code class=codeBlockLines_e6Vv><div class=token-line style=color:#393A34><span class="token plain">wireByteCount = readVarUint32()</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">elementWidth = primitiveWireElementWidth(kind)</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">validate wireByteCount and element alignment</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">elementCount = wireByteCount / elementWidth</span><br/></div><div class=token-line style=color:#393A34><span class="token plain" style=display:inline-block></span><br/></div><div class=token-line style=color:#393A34><span class="token plain">ctx.checkReadableBytes(wireByteCount)</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">result = allocatePrimitiveResult(elementCount)</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">copy or decode wireByteCount bytes from the current readable buffer into result</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">advance the reader index by wireByteCount</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">return result</span><br/></div></code></pre></div></div> |
| <p>Byte values are the <code>elementWidth == 1</code> specialization of the same policy. In |
| that case the serializer shape is:</p> |
| <div class="language-text codeBlockContainer_Ckt0 theme-code-block" style=--prism-color:#393A34;--prism-background-color:#f6f8fa><div class=codeBlockContent_QJqH><pre tabindex=0 class="prism-code language-text codeBlock_bY9V thin-scrollbar" style=color:#393A34;background-color:#f6f8fa><code class=codeBlockLines_e6Vv><div class=token-line style=color:#393A34><span class="token plain">byteCount = readVarUint32()</span><br/></div><div class=token-line style=color:#393A34><span class="token plain" style=display:inline-block></span><br/></div><div class=token-line style=color:#393A34><span class="token plain">ctx.checkReadableBytes(byteCount)</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">result = allocateBytes(byteCount)</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">copy byteCount bytes from the current readable buffer into result</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">advance the reader index by byteCount</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">return result</span><br/></div></code></pre></div></div> |
| <p>This policy avoids three inefficient implementation shapes:</p> |
| <ul> |
| <li class="">allocating the complete final contiguous value before the encoded body is |
| readable</li> |
| <li class="">growing or repeatedly copying the final result container on stream slow paths</li> |
| <li class="">adding serializer-local chunk buffers when the byte owner can prove |
| readability once and expose a normal buffered read</li> |
| </ul> |
| <p>Scratch buffers remain appropriate when the target representation is not a |
| direct byte target, such as string transcoding, compression, byte-order |
| conversion that is not performed in place, bit-packed values, or runtimes whose |
| stream API cannot read into a caller-provided target.</p> |
| <p>For fixed-width primitive arrays, the final result must not become visible to |
| callers until the exact encoded byte count has been read successfully.</p> |
| <p>For list, set, map, and other container readers, the declared logical element |
| count is not an encoded byte count, so serializers must still own all element, |
| chunk, nullability, reference, and type-dispatch semantics. It is still the |
| right allocation proof for count-based preallocation: after validating a |
| non-empty count and reading any serializer-owned header or type metadata that |
| precedes allocation, call <code>checkReadableBytes(logicalCount)</code> before allocating, |
| reserving, or size-hinting from that count. The byte owner handles buffer versus |
| stream readiness; the container serializer then allocates with the declared |
| count and reads elements through its normal owner path.</p> |
| <p>This check is not a full container-body validation. It only prevents a small or |
| truncated input from causing a large count-based preallocation. Chunk sizes, |
| duplicate keys, element value semantics, and protocol strictness remain owned by |
| the container/map serializer and should be validated only when they protect a |
| real owner invariant.</p> |
| <p>For TypeDef or TypeMeta bodies, first prove that the encoded metadata body bytes |
| are readable through the byte owner. Field-list allocation should happen after |
| that body readability check and should not use a separate small initial-capacity |
| cap as a security rule.</p> |
| <p>Skip paths do not need to materialize skipped values. Existing byte-skip |
| operations should consume any available buffered prefix first, then skip or drop |
| remaining stream bytes in bounded steps.</p> |
| <h3 class="anchor anchorTargetStickyNavbar_Vzrq" id=nested-reads-use-readcontext>Nested reads use <code>ReadContext</code><a href=#nested-reads-use-readcontext class=hash-link aria-label="Direct link to nested-reads-use-readcontext" title="Direct link to nested-reads-use-readcontext" translate=no></a></h3> |
| <p>Important rules:</p> |
| <ul> |
| <li class="">serializers that allocate the result object early must call |
| <code>context.reference(obj)</code> before reading nested children that may refer back to |
| it</li> |
| <li class="">nested serializer flow should stay straight-line; do not add internal |
| <code>try/finally</code> blocks just to restore operation-local state</li> |
| <li class="">top-level <code>Fory.deserialize(...)</code> owns the operation reset <code>finally</code></li> |
| </ul> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=depth-tracking>Depth Tracking<a href=#depth-tracking class=hash-link aria-label="Direct link to Depth Tracking" title="Direct link to Depth Tracking" translate=no></a></h2> |
| <p><code>WriteContext</code> and <code>ReadContext</code> track logical object depth explicitly. |
| <code>increaseDepth()</code> enforces <code>Config.maxDepth</code>.</p> |
| <p>Depth should stay explicit on the contexts rather than relying on the native |
| call stack alone. At the same time, depth cleanup should not depend on nested |
| <code>try/finally</code> blocks throughout serializer code. Top-level context reset must be |
| able to recover operation-local state after failures.</p> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=struct-compatibility>Struct Compatibility<a href=#struct-compatibility class=hash-link aria-label="Direct link to Struct Compatibility" title="Direct link to Struct Compatibility" translate=no></a></h2> |
| <p>Struct-specific schema/version framing and compatible-field layout belong in the |
| struct serializer layer, not on <code>Fory</code> and not on the public serializer API.</p> |
| <p>In Dart that internal owner is <code>StructSerializer</code>.</p> |
| <p><code>StructSerializer</code> is responsible for:</p> |
| <ul> |
| <li class="">schema-hash framing when compatibility mode is off and version checks are on</li> |
| <li class="">compatible-struct field remapping when compatibility mode is on</li> |
| <li class="">caching compatible read layouts</li> |
| <li class="">skipping unknown compatible fields</li> |
| <li class="">passing compatible read layouts explicitly to generated serializers</li> |
| <li class="">classifying matched compatible fields as exact direct reads, compatible |
| conversions, or remote-only skips before generated dispatch</li> |
| </ul> |
| <p>When <code>Config.compatible</code> is enabled and the struct is marked evolving:</p> |
| <ul> |
| <li class="">the wire type uses the compatible struct form</li> |
| <li class="">the writer emits shared TypeDef metadata</li> |
| <li class="">reads map incoming fields by identifier and skip unknown fields</li> |
| <li class="">generated serializers apply matched fields directly while preserving their own |
| object construction and default-value rules</li> |
| <li class="">exact matched field schemas use the same direct read shape as same-schema |
| reads and must not receive remote compatible metadata</li> |
| <li class="">matched scalar fields may use compatible scalar conversion only when the |
| layout has classified a remote/local top-level scalar pair as lossless |
| convertible and both field schemas have <code>trackingRef = false</code></li> |
| <li class="">compatible scalar conversion applies only to the immediate matched field. |
| Nested collection, array, map key, and map value schemas must not be accepted |
| by recursively applying scalar conversion to child schemas.</li> |
| <li class="">direct top-level <code>list<T?></code> to dense <code>array<T></code> matched fields must be |
| classified as compatible when element domains match; the nullable element |
| schema bit alone is not a schema-pair rejection. Actual null element payloads |
| fail in the dense-array reader. Ref-tracked list-element framing is separate |
| and may remain rejected when the runtime cannot materialize it without |
| generic/reference paths.</li> |
| </ul> |
| <p>When <code>compatible</code> is disabled and <code>checkStructVersion</code> is enabled:</p> |
| <ul> |
| <li class="">the writer emits the schema hash for struct payloads</li> |
| <li class="">the read side checks that hash before reading fields</li> |
| </ul> |
| <p>Compatible scalar conversion is owned by the compatible struct field reader or |
| the generated compatible layout action. Root facades, read/write contexts, type |
| resolvers, class resolvers, xlang type resolvers, and raw buffer utilities must |
| not expose public conversion APIs or carry conversion state. Resolvers may |
| provide field schema metadata for layout classification, but the conversion |
| decision and value adaptation stay with the serializer-owned compatible field |
| layout. Layout classification must reject top-level scalar conversions when |
| either matched schema has <code>trackingRef = true</code> and must reject same scalar type |
| pairs whose top-level <code>trackingRef</code> framing differs; converters must not add a |
| reference-table path for scalar mismatches. Recursive schema comparison inside |
| containers must reject scalar mismatches instead of reusing the top-level scalar |
| conversion matrix. Generated serializers should consume the classified layout |
| decision directly:</p> |
| <ul> |
| <li class="">source-generated serializers use the layout's matched-field dispatch key to |
| select exact direct field code, compatible conversion code, or skip code</li> |
| <li class="">regenerated serializers may instead compile a remote-schema-specific |
| straight-line reader after classification, without a second outer matched-id |
| switch, when the generated source still has pure direct, pure conversion, and |
| explicit skip operations</li> |
| <li class="">compatible scalar conversion cases must read the concrete remote wire scalar |
| selected by classification and compose only the required lossless conversion; |
| they must not call a generic runtime converter that redispatches by remote and |
| local scalar type IDs, field descriptors, field names, or schema eligibility |
| helpers</li> |
| </ul> |
| <p>Same-schema readers with matching reference and null/optional framing must keep |
| direct scalar read paths without conversion branches or per-field conversion |
| objects. Same raw scalar types with different null/optional framing may still |
| use the compatible nullable/optional composition path when both fields are not |
| reference-tracked.</p> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=meta-strings-and-shared-type-metadata>Meta Strings And Shared Type Metadata<a href=#meta-strings-and-shared-type-metadata class=hash-link aria-label="Direct link to Meta Strings And Shared Type Metadata" title="Direct link to Meta Strings And Shared Type Metadata" translate=no></a></h2> |
| <p>Two explicit pieces of state back xlang type metadata:</p> |
| <ul> |
| <li class=""><code>MetaStringWriter</code> and <code>MetaStringReader</code> deduplicate and decode namespace |
| and type-name strings</li> |
| <li class="">shared TypeDef write/read state tracks announced compatible struct metadata</li> |
| </ul> |
| <p>Ownership rules:</p> |
| <ul> |
| <li class="">canonical encoded names live in <code>TypeResolver</code></li> |
| <li class="">per-operation dynamic meta-string ids live on <code>MetaStringWriter</code> and |
| <code>MetaStringReader</code></li> |
| <li class="">shared type-definition tables are operation-local context state</li> |
| </ul> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=enums-in-xlang-mode>Enums In Xlang Mode<a href=#enums-in-xlang-mode class=hash-link aria-label="Direct link to Enums In Xlang Mode" title="Direct link to Enums In Xlang Mode" translate=no></a></h2> |
| <p>In xlang mode, enums are serialized by numeric tag, not by name.</p> |
| <p>In Java:</p> |
| <ul> |
| <li class="">the default tag is the declaration ordinal</li> |
| <li class=""><code>@ForyEnumId</code> can override that with a stable explicit tag</li> |
| <li class=""><code>serializeEnumByName(true)</code> affects native Java mode, not xlang mode</li> |
| </ul> |
| <p>Other language implementations should preserve the same wire rule even if the configuration or |
| annotation surface differs.</p> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=out-of-band-buffer-objects>Out-Of-Band Buffer Objects<a href=#out-of-band-buffer-objects class=hash-link aria-label="Direct link to Out-Of-Band Buffer Objects" title="Direct link to Out-Of-Band Buffer Objects" translate=no></a></h2> |
| <p>Buffer-object handling follows the same split:</p> |
| <ul> |
| <li class="">one root bit advertises whether out-of-band buffers are in play</li> |
| <li class="">nested buffer-object payloads still decide in-band vs out-of-band one value at |
| a time</li> |
| <li class="">serializers use read/write context helpers rather than bypassing the context layer</li> |
| </ul> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=code-generation>Code Generation<a href=#code-generation class=hash-link aria-label="Direct link to Code Generation" title="Direct link to Code Generation" translate=no></a></h2> |
| <p>The normal Dart integration path is:</p> |
| <ol> |
| <li class="">annotate structs with <code>@ForyStruct</code></li> |
| <li class="">annotate field overrides with <code>@ForyField</code></li> |
| <li class="">run <code>build_runner</code></li> |
| <li class="">call the generated per-library helper, such as |
| <code><InputFile>Fory.register(...)</code>, to bind private generated metadata and |
| register generated types</li> |
| </ol> |
| <p>Generated code should emit:</p> |
| <ul> |
| <li class="">private serializer classes</li> |
| <li class="">private metadata constants</li> |
| <li class="">a public per-library registration helper that users call from application code</li> |
| <li class="">private generated installation helpers that keep serializer factories private</li> |
| </ul> |
| <p>The public helper should be a thin generated wrapper around the Fory |
| registration API, not a public global registry or a second unrelated |
| registration API family.</p> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=directory-layout>Directory Layout<a href=#directory-layout class=hash-link aria-label="Direct link to Directory Layout" title="Direct link to Directory Layout" translate=no></a></h2> |
| <p>Under each Dart package <code>lib/</code> tree, only one nested source layer is allowed.</p> |
| <p>Allowed:</p> |
| <ul> |
| <li class=""><code>lib/fory.dart</code></li> |
| <li class=""><code>lib/src/<file>.dart</code></li> |
| <li class=""><code>lib/src/<area>/<file>.dart</code></li> |
| </ul> |
| <p>Not allowed:</p> |
| <ul> |
| <li class=""><code>lib/src/<area>/<subarea>/<file>.dart</code></li> |
| </ul> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=serializer-design-rules-for-new-implementations>Serializer Design Rules For New Implementations<a href=#serializer-design-rules-for-new-implementations class=hash-link aria-label="Direct link to Serializer Design Rules For New Implementations" title="Direct link to Serializer Design Rules For New Implementations" translate=no></a></h2> |
| <p>Any new xlang implementation should follow these rules even if its surface API looks |
| different:</p> |
| <ol> |
| <li class="">Keep root operations on the <code>Fory</code> facade and nested payload work on |
| explicit read and write contexts.</li> |
| <li class="">Keep reference tracking behind dedicated read-side and write-side services |
| so the disabled path stays cheap.</li> |
| <li class="">Make serializers payload-only. Type metadata, registration, and root |
| framing belong to the <code>Fory</code> and type resolver layers.</li> |
| <li class="">Track per-operation state explicitly. Do not rely on ambient thread-local |
| instance state.</li> |
| <li class="">Reserve read reference IDs before materializing new objects, and bind |
| partially built objects as soon as a nested child may refer back to them.</li> |
| <li class="">Keep operation setup and operation cleanup separate. <code>prepare(...)</code> binds |
| the current operation inputs, and <code>reset()</code> clears operation-local state.</li> |
| <li class="">Preserve the separation between the root bitmap, per-object ref flags, type |
| headers, and payload bytes.</li> |
| <li class="">Keep internal naming in the serialization domain. Prefer words like |
| <code>serializer</code>, <code>binding</code>, and <code>layout</code>; avoid RPC-style terms such as |
| <code>session</code> or vague control-flow terms such as <code>plan</code>.</li> |
| <li class="">After any xlang protocol or ownership change, run the cross-language test |
| matrix and update both this guide and |
| <a class="" href=/docs/1.2.0/specification/xlang_serialization_spec>Xlang Serialization Spec</a>.</li> |
| </ol> |
| <h2 class="anchor anchorTargetStickyNavbar_Vzrq" id=validation>Validation<a href=#validation class=hash-link aria-label="Direct link to Validation" title="Direct link to Validation" translate=no></a></h2> |
| <p>For Dart implementation changes, run at minimum:</p> |
| <div class="language-bash codeBlockContainer_Ckt0 theme-code-block" style=--prism-color:#393A34;--prism-background-color:#f6f8fa><div class=codeBlockContent_QJqH><pre tabindex=0 class="prism-code language-bash codeBlock_bY9V thin-scrollbar" style=color:#393A34;background-color:#f6f8fa><code class=codeBlockLines_e6Vv><div class=token-line style=color:#393A34><span class="token builtin class-name">cd</span><span class="token plain"> dart</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">dart run build_runner build --delete-conflicting-outputs</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">dart analyze</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">dart </span><span class="token builtin class-name">test</span><br/></div></code></pre></div></div> |
| <p>For generated consumer coverage, also run:</p> |
| <div class="language-bash codeBlockContainer_Ckt0 theme-code-block" style=--prism-color:#393A34;--prism-background-color:#f6f8fa><div class=codeBlockContent_QJqH><pre tabindex=0 class="prism-code language-bash codeBlock_bY9V thin-scrollbar" style=color:#393A34;background-color:#f6f8fa><code class=codeBlockLines_e6Vv><div class=token-line style=color:#393A34><span class="token builtin class-name">cd</span><span class="token plain"> dart/packages/fory-test</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">dart run build_runner build --delete-conflicting-outputs</span><br/></div><div class=token-line style=color:#393A34><span class="token plain">dart </span><span class="token builtin class-name">test</span><br/></div></code></pre></div></div></div><footer class="theme-doc-footer docusaurus-mt-lg"><div class="row margin-top--sm theme-doc-footer-edit-meta-row"><div class="col noPrint_WFHX"><a 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| <p> |
| Copyright © 2026 The Apache Software Foundation, Licensed under the Apache License, Version 2.0. <br/> |
| Apache Fory, Fory, Apache, the Apache Logo and the Apache Fory logo are either registered trademarks or trademarks of the Apache Software Foundation in the United States and/or other countries. |
| </p> |
| </div></div></div></div></footer></div></body> |
