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| <div class="section" id="characteristic-access"> |
| <h1>Characteristic Access<a class="headerlink" href="#characteristic-access" title="Permalink to this headline">¶</a></h1> |
| <div class="contents local topic" id="contents"> |
| <ul class="simple"> |
| <li><p><a class="reference internal" href="#review" id="id1">Review</a></p></li> |
| <li><p><a class="reference internal" href="#function-signature" id="id2">Function signature</a></p></li> |
| <li><p><a class="reference internal" href="#determine-characteristic-being-accessed" id="id3">Determine characteristic being accessed</a></p></li> |
| <li><p><a class="reference internal" href="#read-access" id="id4">Read access</a></p></li> |
| <li><p><a class="reference internal" href="#write-access" id="id5">Write access</a></p></li> |
| </ul> |
| </div> |
| <div class="section" id="review"> |
| <h2><a class="toc-backref" href="#id1">Review</a><a class="headerlink" href="#review" title="Permalink to this headline">¶</a></h2> |
| <p>A characteristic’s access callback implements its behavior. Recall that |
| services and characteristics are registered with NimBLE via attribute |
| tables. Each characteristic definition in an attribute table contains an |
| <em>access_cb</em> field. The <em>access_cb</em> field is an application callback |
| that gets executed whenever a peer device attempts to read or write the |
| characteristic.</p> |
| <p>Earlier in this tutorial, we looked at how <em>bleprph</em> implements the GAP |
| service. Let’s take another look at how <em>bleprph</em> specifies the first |
| few characteristics in this service.</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">static</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">ble_gatt_svc_def</span><span class="w"> </span><span class="n">gatt_svr_svcs</span><span class="p">[]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="cm">/*** Service: Security test. */</span> |
| <span class="w"> </span><span class="p">.</span><span class="n">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BLE_GATT_SVC_TYPE_PRIMARY</span><span class="p">,</span> |
| <span class="w"> </span><span class="p">.</span><span class="n">uuid</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">&</span><span class="n">gatt_svr_svc_sec_test_uuid</span><span class="p">.</span><span class="n">u</span><span class="p">,</span> |
| <span class="w"> </span><span class="p">.</span><span class="n">characteristics</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="k">struct</span><span class="w"> </span><span class="nc">ble_gatt_chr_def</span><span class="p">[])</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="cm">/*** Characteristic: Random number generator. */</span> |
| <span class="w"> </span><span class="p">.</span><span class="n">uuid</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">&</span><span class="n">gatt_svr_chr_sec_test_rand_uuid</span><span class="p">.</span><span class="n">u</span><span class="p">,</span> |
| <span class="w"> </span><span class="p">.</span><span class="n">access_cb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">gatt_svr_chr_access_sec_test</span><span class="p">,</span> |
| <span class="w"> </span><span class="p">.</span><span class="n">flags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BLE_GATT_CHR_F_READ</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">BLE_GATT_CHR_F_READ_ENC</span><span class="p">,</span> |
| <span class="w"> </span><span class="p">},</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="cm">/*** Characteristic: Static value. */</span> |
| <span class="w"> </span><span class="p">.</span><span class="n">uuid</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">gatt_svr_chr_sec_test_static_uuid</span><span class="p">.</span><span class="n">u</span><span class="p">,</span> |
| <span class="w"> </span><span class="p">.</span><span class="n">access_cb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">gatt_svr_chr_access_sec_test</span><span class="p">,</span> |
| <span class="w"> </span><span class="p">.</span><span class="n">flags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BLE_GATT_CHR_F_READ</span><span class="w"> </span><span class="o">|</span> |
| <span class="w"> </span><span class="n">BLE_GATT_CHR_F_WRITE</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">BLE_GATT_CHR_F_WRITE_ENC</span><span class="p">,</span> |
| <span class="w"> </span><span class="p">},</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="c1">// [...]</span> |
| </pre></div> |
| </div> |
| <p>As you can see, <em>bleprph</em> uses the same <em>access_cb</em> function for all |
| the GAP service characteristics, but the developer could have |
| implemented separate functions for each characteristic if they |
| preferred. Here is the <em>access_cb</em> function that the GAP service |
| characteristics use:</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">static</span><span class="w"> </span><span class="kt">int</span> |
| <span class="nf">gatt_svr_chr_access_sec_test</span><span class="p">(</span><span class="kt">uint16_t</span><span class="w"> </span><span class="n">conn_handle</span><span class="p">,</span><span class="w"> </span><span class="kt">uint16_t</span><span class="w"> </span><span class="n">attr_handle</span><span class="p">,</span> |
| <span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">ble_gatt_access_ctxt</span><span class="w"> </span><span class="o">*</span><span class="n">ctxt</span><span class="p">,</span> |
| <span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">arg</span><span class="p">)</span> |
| <span class="p">{</span> |
| <span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">ble_uuid_t</span><span class="w"> </span><span class="o">*</span><span class="n">uuid</span><span class="p">;</span> |
| <span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">rand_num</span><span class="p">;</span> |
| <span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">rc</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="n">uuid</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ctxt</span><span class="o">-></span><span class="n">chr</span><span class="o">-></span><span class="n">uuid</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="cm">/* Determine which characteristic is being accessed by examining its</span> |
| <span class="cm"> * 128-bit UUID.</span> |
| <span class="cm"> */</span> |
| |
| <span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">ble_uuid_cmp</span><span class="p">(</span><span class="n">uuid</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">gatt_svr_chr_sec_test_rand_uuid</span><span class="p">.</span><span class="n">u</span><span class="p">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="n">assert</span><span class="p">(</span><span class="n">ctxt</span><span class="o">-></span><span class="n">op</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">BLE_GATT_ACCESS_OP_READ_CHR</span><span class="p">);</span> |
| |
| <span class="w"> </span><span class="cm">/* Respond with a 32-bit random number. */</span> |
| <span class="w"> </span><span class="n">rand_num</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">rand</span><span class="p">();</span> |
| <span class="w"> </span><span class="n">rc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">os_mbuf_append</span><span class="p">(</span><span class="n">ctxt</span><span class="o">-></span><span class="n">om</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">rand_num</span><span class="p">,</span><span class="w"> </span><span class="k">sizeof</span><span class="w"> </span><span class="n">rand_num</span><span class="p">);</span> |
| <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">rc</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">?</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">BLE_ATT_ERR_INSUFFICIENT_RES</span><span class="p">;</span> |
| <span class="w"> </span><span class="p">}</span> |
| |
| <span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">ble_uuid_cmp</span><span class="p">(</span><span class="n">uuid</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">gatt_svr_chr_sec_test_static_uuid</span><span class="p">.</span><span class="n">u</span><span class="p">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="k">switch</span><span class="w"> </span><span class="p">(</span><span class="n">ctxt</span><span class="o">-></span><span class="n">op</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="no">BLE_GATT_ACCESS_OP_READ_CHR</span><span class="p">:</span> |
| <span class="w"> </span><span class="n">rc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">os_mbuf_append</span><span class="p">(</span><span class="n">ctxt</span><span class="o">-></span><span class="n">om</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">gatt_svr_sec_test_static_val</span><span class="p">,</span> |
| <span class="w"> </span><span class="k">sizeof</span><span class="w"> </span><span class="n">gatt_svr_sec_test_static_val</span><span class="p">);</span> |
| <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">rc</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">?</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">BLE_ATT_ERR_INSUFFICIENT_RES</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="no">BLE_GATT_ACCESS_OP_WRITE_CHR</span><span class="p">:</span> |
| <span class="w"> </span><span class="n">rc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">gatt_svr_chr_write</span><span class="p">(</span><span class="n">ctxt</span><span class="o">-></span><span class="n">om</span><span class="p">,</span> |
| <span class="w"> </span><span class="k">sizeof</span><span class="w"> </span><span class="n">gatt_svr_sec_test_static_val</span><span class="p">,</span> |
| <span class="w"> </span><span class="k">sizeof</span><span class="w"> </span><span class="n">gatt_svr_sec_test_static_val</span><span class="p">,</span> |
| <span class="w"> </span><span class="o">&</span><span class="n">gatt_svr_sec_test_static_val</span><span class="p">,</span><span class="w"> </span><span class="nb">NULL</span><span class="p">);</span> |
| <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">rc</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="k">default</span><span class="o">:</span> |
| <span class="w"> </span><span class="n">assert</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span> |
| <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">BLE_ATT_ERR_UNLIKELY</span><span class="p">;</span> |
| <span class="w"> </span><span class="p">}</span> |
| <span class="w"> </span><span class="p">}</span> |
| |
| <span class="w"> </span><span class="cm">/* Unknown characteristic; the nimble stack should not have called this</span> |
| <span class="cm"> * function.</span> |
| <span class="cm"> */</span> |
| <span class="w"> </span><span class="n">assert</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span> |
| <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">BLE_ATT_ERR_UNLIKELY</span><span class="p">;</span> |
| <span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>After you’ve taken a moment to examine the structure of this function, |
| let’s explore some details.</p> |
| </div> |
| <div class="section" id="function-signature"> |
| <h2><a class="toc-backref" href="#id2">Function signature</a><a class="headerlink" href="#function-signature" title="Permalink to this headline">¶</a></h2> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">static</span><span class="w"> </span><span class="kt">int</span> |
| <span class="n">gatt_svr_chr_access_sec_test</span><span class="p">(</span><span class="kt">uint16_t</span><span class="w"> </span><span class="n">conn_handle</span><span class="p">,</span><span class="w"> </span><span class="kt">uint16_t</span><span class="w"> </span><span class="n">attr_handle</span><span class="p">,</span> |
| <span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">ble_gatt_access_ctxt</span><span class="w"> </span><span class="o">*</span><span class="n">ctxt</span><span class="p">,</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">arg</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>A characteristic access function always takes this same set of |
| parameters and always returns an int. The parameters to this function |
| type are documented below.</p> |
| <table class="docutils align-default"> |
| <colgroup> |
| <col style="width: 38%" /> |
| <col style="width: 33%" /> |
| <col style="width: 29%" /> |
| </colgroup> |
| <thead> |
| <tr class="row-odd"><th class="head"><p><strong>Parameter</strong></p></th> |
| <th class="head"><p><strong>Purpose</strong></p></th> |
| <th class="head"><p><strong>Notes</strong></p></th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr class="row-even"><td><p>conn_handle</p></td> |
| <td><p>Indicates |
| which |
| connection |
| the |
| characterist |
| ic |
| access was |
| sent over.</p></td> |
| <td><p>Use this |
| value to |
| determine |
| which peer |
| is |
| accessing |
| the |
| characteri |
| stic.</p></td> |
| </tr> |
| <tr class="row-odd"><td><p>attr_handle</p></td> |
| <td><p>The |
| low-level |
| ATT handle |
| of the |
| characterist |
| ic |
| value |
| attribute.</p></td> |
| <td><p>Can be |
| used to |
| determine |
| which |
| characteri |
| stic |
| is being |
| accessed |
| if you |
| don’t want |
| to perform |
| a UUID |
| lookup.</p></td> |
| </tr> |
| <tr class="row-even"><td><p>ctxt</p></td> |
| <td><p>Contains the |
| characterist |
| ic |
| value |
| pointer that |
| the |
| application |
| needs to |
| access.</p></td> |
| <td><p>For |
| characteri |
| stic |
| accesses, |
| use the |
| <em>ctxt->chr |
| _access</em> |
| member; |
| for |
| descriptor |
| accesses, |
| use the |
| <em>ctxt->dsc |
| _access</em> |
| member.</p></td> |
| </tr> |
| </tbody> |
| </table> |
| <p>The return value of the access function tells the NimBLE stack how to |
| respond to the peer performing the operation. A value of 0 indicates |
| success. For failures, the function returns the specific ATT error code |
| that the NimBLE stack should respond with. The ATT error codes are |
| defined in |
| <a class="reference external" href="https://github.com/apache/incubator-mynewt-core/blob/master/net/nimble/host/include/host/ble_att.h">net/nimble/host/include/host/ble_att.h</a>.</p> |
| </div> |
| <div class="section" id="determine-characteristic-being-accessed"> |
| <h2><a class="toc-backref" href="#id3">Determine characteristic being accessed</a><a class="headerlink" href="#determine-characteristic-being-accessed" title="Permalink to this headline">¶</a></h2> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">ble_uuid_cmp</span><span class="p">(</span><span class="n">uuid</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">gatt_svr_chr_sec_test_rand_uuid</span><span class="p">.</span><span class="n">u</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>The function compares UUID with UUIDs of characteristic - if it fits, |
| characteristic is being accessed. There are two alternative methods <em>bleprph</em> |
| could have used to accomplish this task:</p> |
| <ul class="simple"> |
| <li><p>Map characteristics to ATT handles during service registration; use |
| the <em>attr_handle</em> parameter as a key into this table during |
| characteristic access.</p></li> |
| <li><p>Implement a dedicated function for each characteristic; each function |
| inherently knows which characteristic it corresponds to.</p></li> |
| </ul> |
| </div> |
| <div class="section" id="read-access"> |
| <h2><a class="toc-backref" href="#id4">Read access</a><a class="headerlink" href="#read-access" title="Permalink to this headline">¶</a></h2> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">case</span><span class="w"> </span><span class="no">BLE_GATT_ACCESS_OP_READ_CHR</span><span class="p">:</span> |
| <span class="w"> </span><span class="n">rc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">os_mbuf_append</span><span class="p">(</span><span class="n">ctxt</span><span class="o">-></span><span class="n">om</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">gatt_svr_sec_test_static_val</span><span class="p">,</span> |
| <span class="w"> </span><span class="k">sizeof</span><span class="w"> </span><span class="n">gatt_svr_sec_test_static_val</span><span class="p">);</span> |
| <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">rc</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">?</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">BLE_ATT_ERR_INSUFFICIENT_RES</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| <p>This code excerpt handles read accesses to the device characteristic. |
| <em>ctxt->om</em> is chained memory buffer that for reads is being populated |
| with characteristic data. Returned value is either 0 for success or |
| <em>BLE_ATT_ERR_INSUFFICIENT_RES</em> if failed. The check makes sure the |
| NimBLE stack is doing its job; this characteristic was registered as |
| read-only, so the stack should have prevented write accesses.</p> |
| </div> |
| <div class="section" id="write-access"> |
| <h2><a class="toc-backref" href="#id5">Write access</a><a class="headerlink" href="#write-access" title="Permalink to this headline">¶</a></h2> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">static</span><span class="w"> </span><span class="kt">int</span> |
| <span class="nf">gatt_svr_chr_write</span><span class="p">(</span><span class="k">struct</span><span class="w"> </span><span class="nc">os_mbuf</span><span class="w"> </span><span class="o">*</span><span class="n">om</span><span class="p">,</span><span class="w"> </span><span class="kt">uint16_t</span><span class="w"> </span><span class="n">min_len</span><span class="p">,</span><span class="w"> </span><span class="kt">uint16_t</span><span class="w"> </span><span class="n">max_len</span><span class="p">,</span> |
| <span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">dst</span><span class="p">,</span><span class="w"> </span><span class="kt">uint16_t</span><span class="w"> </span><span class="o">*</span><span class="n">len</span><span class="p">)</span> |
| <span class="p">{</span> |
| <span class="w"> </span><span class="kt">uint16_t</span><span class="w"> </span><span class="n">om_len</span><span class="p">;</span> |
| <span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">rc</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="n">om_len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">OS_MBUF_PKTLEN</span><span class="p">(</span><span class="n">om</span><span class="p">);</span> |
| <span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">om_len</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="n">min_len</span><span class="w"> </span><span class="o">||</span><span class="w"> </span><span class="n">om_len</span><span class="w"> </span><span class="o">></span><span class="w"> </span><span class="n">max_len</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">BLE_ATT_ERR_INVALID_ATTR_VALUE_LEN</span><span class="p">;</span> |
| <span class="w"> </span><span class="p">}</span> |
| |
| <span class="w"> </span><span class="n">rc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ble_hs_mbuf_to_flat</span><span class="p">(</span><span class="n">om</span><span class="p">,</span><span class="w"> </span><span class="n">dst</span><span class="p">,</span><span class="w"> </span><span class="n">max_len</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p">);</span> |
| <span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">rc</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">BLE_ATT_ERR_UNLIKELY</span><span class="p">;</span> |
| <span class="w"> </span><span class="p">}</span> |
| |
| <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span> |
| <span class="p">}</span> |
| <span class="c1">// [...]</span> |
| <span class="k">case</span><span class="w"> </span><span class="no">BLE_GATT_ACCESS_OP_WRITE_CHR</span><span class="p">:</span> |
| <span class="w"> </span><span class="n">rc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">gatt_svr_chr_write</span><span class="p">(</span><span class="n">ctxt</span><span class="o">-></span><span class="n">om</span><span class="p">,</span> |
| <span class="w"> </span><span class="k">sizeof</span><span class="w"> </span><span class="n">gatt_svr_sec_test_static_val</span><span class="p">,</span> |
| <span class="w"> </span><span class="k">sizeof</span><span class="w"> </span><span class="n">gatt_svr_sec_test_static_val</span><span class="p">,</span> |
| <span class="w"> </span><span class="o">&</span><span class="n">gatt_svr_sec_test_static_val</span><span class="p">,</span><span class="w"> </span><span class="nb">NULL</span><span class="p">);</span> |
| <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">rc</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| <p>This code excerpt handles writes to the Static value |
| characteristic. This characteristic was registered as read-write, so the |
| <em>return rc</em> here is just a safety precaution to ensure the NimBLE stack |
| is doing its job.</p> |
| <p>Data is written to the <em>ctxt->om</em> buffer from <em>gatt_svr_sec_test_static_val</em> |
| by <code class="docutils literal notranslate"><span class="pre">ble_hs_mbuf_to_flat()</span></code> function. If length of written data greater or |
| smaller than length of <em>gatt_svr_sec_test_static_val</em>, function return error.</p> |
| <p>Many characteristics have strict length requirements for write |
| operations.</p> |
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