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httplib.html

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  3. <title>The HTTP library - Boost.Outcome documentation</title>
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    13. 

  13.   <div class="titlepage"><div><div><h1 style="clear: both">The HTTP library</h1></div></div></div>
    14. 

  14.   <p>Let us imagine a simple application: it fetches a HTTP page using a HTTP library,
    15. 

  15. sends it through HTML tidy via the htmltidy library, and then writes it to disc
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  16. using a filelib library. So three third party libraries, two using Outcome in
    17. 

  17. incompatible ways, and the third being a C library just for kicks.</p>
    18. 

  18. 

  19. <p>Let us imagine that the HTTP library has the following public interface:</p>
    20. 

  20. 

  21. <div class="code-snippet"><div class="highlight"><pre class="chroma"><code class="language-c++" data-lang="c++"><span class="c1">// This is some standalone library implementing high level HTTP
    22. 

  22. </span><span class="c1"></span><span class="k">namespace</span> <span class="n">httplib</span>
    23. 

  23. <span class="p">{</span>
    24. 

  24.   <span class="c1">// These are the error code that this HTTP library can return
    25. 

  25. </span><span class="c1"></span>  <span class="k">enum</span> <span class="k">class</span><span class="err"> </span><span class="nc">status_code</span>
    26. 

  26.   <span class="p">{</span>
    27. 

  27.     <span class="n">success</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span>  <span class="c1">// not the HTTP success code of 200
    28. 

  28. </span><span class="c1"></span>
    29. 

  29.     <span class="c1">// A subset of all HTTP status codes for brevity
    30. 

  30. </span><span class="c1"></span>    <span class="n">bad_request</span> <span class="o">=</span> <span class="mi">400</span><span class="p">,</span>
    31. 

  31.     <span class="n">access_denied</span> <span class="o">=</span> <span class="mi">401</span><span class="p">,</span>
    32. 

  32.     <span class="n">logon_failed</span> <span class="o">=</span> <span class="mi">402</span><span class="p">,</span>
    33. 

  33.     <span class="n">forbidden</span> <span class="o">=</span> <span class="mi">403</span><span class="p">,</span>
    34. 

  34.     <span class="n">not_found</span> <span class="o">=</span> <span class="mi">404</span><span class="p">,</span>
    35. 

  35.     <span class="n">internal_error</span> <span class="o">=</span> <span class="mi">500</span>
    36. 

  36.   <span class="p">};</span>
    37. 

  37.   <span class="c1">// This is the error type that this HTTP library can return
    38. 

  38. </span><span class="c1"></span>  <span class="k">struct</span> <span class="n">failure</span>
    39. 

  39.   <span class="p">{</span>
    40. 

  40.     <span class="n">status_code</span> <span class="n">status</span><span class="p">{</span><span class="n">status_code</span><span class="o">::</span><span class="n">success</span><span class="p">};</span>
    41. 

  41.     <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">url</span><span class="p">{};</span>  <span class="c1">// The failing URL
    42. 

  42. </span><span class="c1"></span>  <span class="p">};</span>
    43. 

  43.   <span class="c1">// Localise a result implementation to this library, holding
    44. 

  44. </span><span class="c1"></span>  <span class="c1">// the logic error of incorrect observation to mean program
    45. 

  45. </span><span class="c1"></span>  <span class="c1">// termination.
    46. 

  46. </span><span class="c1"></span>  <span class="k">template</span> <span class="o">&lt;</span><span class="k">class</span><span class="err"> </span><span class="nc">T</span><span class="o">&gt;</span>
    47. 

  47.   <span class="k">using</span> <span class="n">result</span> <span class="o">=</span>  <span class="c1">//
    48. 

  48. </span><span class="c1"></span>  <span class="n">BOOST_OUTCOME_V2_NAMESPACE</span><span class="o">::</span><span class="n">result</span><span class="o">&lt;</span><span class="n">T</span><span class="p">,</span> <span class="n">failure</span><span class="p">,</span> <span class="n">BOOST_OUTCOME_V2_NAMESPACE</span><span class="o">::</span><span class="n">policy</span><span class="o">::</span><span class="n">terminate</span><span class="o">&gt;</span><span class="p">;</span>
    49. 

  49. 

  50.   <span class="cm">/* Performs a HTTP GET on the url, returning the body if successful,
    51. 

  51. </span><span class="cm">  a failure with status_code if unsuccessful at the HTTP level, or a
    52. 

  52. </span><span class="cm">  C++ exception throw if something catastrophic happened e.g. bad_alloc
    53. 

  53. </span><span class="cm">  */</span>
    54. 

  54.   <span class="n">result</span><span class="o">&lt;</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&gt;</span> <span class="n">get</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">url</span><span class="p">);</span>
    55. 

  55. <span class="p">}</span>  <span class="c1">// namespace httplib
    56. 

  56. </span><span class="c1"></span></code></pre></div><a href="https://github.com/boostorg/outcome/tree/master/doc/src/snippets/finale.cpp#L40" class="code-snippet-url" target="_blank">View this code on Github</a></div>
    57. 

  57. 

  58. 

  59. <p>The HTTP library is a mixed-failure design. Likely failures (HTTP status codes)
    60. 

  60. are returned via <code>httplib::failure</code>, unlikely failures (e.g. out of memory)
    61. 

  61. are returned via throw of the usual STL exception types.</p>
    62. 

  62. 

  63. <p>The sole API we bother describing is an implementation of HTTP GET. It fetches
    64. 

  64. a URL, and either returns the contents or the failure reason why not.</p>
    65. 

  65. 

  66. 

  67.         </div><p><small>Last revised: February 08, 2019 at 22:18:08 UTC</small></p>
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