--- /dev/null
+#include <stdlib.h>
+#include <string.h>
+
+#include <jansson.h>
+#include <curl/curl.h>
+
+#define BUFFER_SIZE (256 * 1024) /* 256 KB */
+
+#define URL_FORMAT "http://github.com/api/v2/json/commits/list/%s/%s/master"
+#define URL_SIZE 256
+
+/* Return the offset of the first newline in text or the length of
+ text if there's no newline */
+static int newline_offset(const char *text)
+{
+ const char *newline = strchr(text, '\n');
+ if(!newline)
+ return strlen(text);
+ else
+ return (int)(newline - text);
+}
+
+struct write_result
+{
+ char *data;
+ int pos;
+};
+
+static size_t write_response(void *ptr, size_t size, size_t nmemb, void *stream)
+{
+ struct write_result *result = (struct write_result *)stream;
+
+ if(result->pos + size * nmemb >= BUFFER_SIZE - 1)
+ {
+ fprintf(stderr, "error: too small buffer\n");
+ return 0;
+ }
+
+ memcpy(result->data + result->pos, ptr, size * nmemb);
+ result->pos += size * nmemb;
+
+ return size * nmemb;
+}
+
+static char *request(const char *url)
+{
+ CURL *curl;
+ CURLcode status;
+ char *data;
+ long code;
+
+ curl = curl_easy_init();
+ data = malloc(BUFFER_SIZE);
+ if(!curl || !data)
+ return NULL;
+
+ struct write_result write_result = {
+ .data = data,
+ .pos = 0
+ };
+
+ curl_easy_setopt(curl, CURLOPT_URL, url);
+ curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_response);
+ curl_easy_setopt(curl, CURLOPT_WRITEDATA, &write_result);
+
+ status = curl_easy_perform(curl);
+ if(status != 0)
+ {
+ fprintf(stderr, "error: unable to request data from %s:\n", url);
+ fprintf(stderr, "%s\n", curl_easy_strerror(status));
+ return NULL;
+ }
+
+ curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &code);
+ if(code != 200)
+ {
+ fprintf(stderr, "error: server responded with code %ld\n", code);
+ return NULL;
+ }
+
+ curl_easy_cleanup(curl);
+ curl_global_cleanup();
+
+ /* zero-terminate the result */
+ data[write_result.pos] = '\0';
+
+ return data;
+}
+
+int main(int argc, char *argv[])
+{
+ unsigned int i;
+ char *text;
+ char url[URL_SIZE];
+
+ json_t *root;
+ json_error_t error;
+ json_t *commits;
+
+ if(argc != 3)
+ {
+ fprintf(stderr, "usage: %s USER REPOSITORY\n\n", argv[0]);
+ fprintf(stderr, "List commits at USER's REPOSITORY.\n\n");
+ return 2;
+ }
+
+ snprintf(url, URL_SIZE, URL_FORMAT, argv[1], argv[2]);
+
+ text = request(url);
+ if(!text)
+ return 1;
+
+ root = json_loads(text, &error);
+ free(text);
+
+ if(!root)
+ {
+ fprintf(stderr, "error: on line %d: %s\n", error.line, error.text);
+ return 1;
+ }
+
+ commits = json_object_get(root, "commits");
+ if(!commits || !json_is_array(commits))
+ {
+ fprintf(stderr, "error: commits is not an array\n");
+ return 1;
+ }
+
+ for(i = 0; i < json_array_size(commits); i++)
+ {
+ json_t *commit, *id, *message;
+ const char *message_text;
+
+ commit = json_array_get(commits, i);
+ if(!json_is_object(commit))
+ {
+ fprintf(stderr, "error: commit %d is not an object\n", i + 1);
+ return 1;
+ }
+
+ id = json_object_get(commit, "id");
+ if(!id || !json_is_string(id))
+ {
+ fprintf(stderr, "error: commit %d: id is not a string\n", i + 1);
+ return 1;
+ }
+
+ message = json_object_get(commit, "message");
+ if(!message || !json_is_string(message))
+ {
+ fprintf(stderr, "error: commit %d: message is not a string\n", i + 1);
+ return 1;
+ }
+
+ message_text = json_string_value(message);
+ printf("%.8s %.*s\n",
+ json_string_value(id),
+ newline_offset(message_text),
+ message_text);
+ }
+
+ json_decref(root);
+ return 0;
+}
--- /dev/null
+.. _tutorial:
+
+********
+Tutorial
+********
+
+.. highlight:: c
+
+In this tutorial, we create a program that fetches the latest commits
+of a repository in GitHub_ over the web. One of the response formats
+supported by `GitHub API`_ is JSON, so the result can be parsed using
+Jansson.
+
+To stick to the the scope of this tutorial, we will only cover the the
+parts of the program related to handling JSON data. For the best user
+experience, the full source code is available:
+:download:`github_commits.c`. To compile it (on Unix-like systems with
+gcc), use the following command::
+
+ gcc -o github_commits github_commits.c -ljansson -lcurl
+
+libcurl_ is used to communicate over the web, so it is required to
+compile the program.
+
+The command line syntax is::
+
+ github_commits USER REPOSITORY
+
+``USER`` is a GitHub user ID and ``REPOSITORY`` is the repository
+name. Please note that the GitHub API is rate limited, so if you run
+the program too many times within a short period of time, the sever
+starts to respond with an error.
+
+.. _GitHub: http://github.com/
+.. _GitHub API: http://develop.github.com/
+.. _libcurl: http://curl.haxx.se/
+
+
+.. _tutorial-github-commits-api:
+
+The GitHub Commits API
+======================
+
+The GitHub commits API is used by sending HTTP requests to URLs
+starting with ``http://github.com/api/v2/json/commits/``. Our program
+only lists the latest commits, so the rest of the URL is
+``list/USER/REPOSITORY/BRANCH``, where ``USER``, ``REPOSITORY`` and
+``BRANCH`` are the GitHub user ID, the name of the repository, and the
+name of the branch whose commits are to be listed, respectively. The
+following definitions are used to build the request URL::
+
+ #define URL_FORMAT "http://github.com/api/v2/json/commits/list/%s/%s/master"
+ #define URL_SIZE 256
+
+GitHub responds with a JSON object of the following form:
+
+.. code-block:: none
+
+ {
+ "commits": [
+ {
+ "id": "<the commit ID>",
+ "message": "<the commit message>",
+ <more fields, not important to this tutorial>
+ },
+ {
+ "id": "<the commit ID>",
+ "message": "<the commit message>",
+ <more fields, not important to this tutorial>
+ },
+ <more commits...>
+ ]
+ }
+
+In our program, the HTTP request is sent using the following
+function::
+
+ static char *request(const char *url);
+
+It takes the URL as a parameter, preforms a HTTP GET request, and
+returns a newly allocated string that contains the response body. For
+full details, refer to :download:`the code <github_commits.c>`, as the
+actual implementation is not important here.
+
+
+.. _tutorial-the-program:
+
+The Program
+===========
+
+First the includes::
+
+ #include <string.h>
+ #include <jansson.h>
+
+Like all the programs using Jansson, we need to include
+:file:`jansson.h`.
+
+The following function is used when formatting the result to find the
+first newline in the commit message::
+
+ /* Return the offset of the first newline in text or the length of
+ text if there's no newline */
+ static int newline_offset(const char *text)
+ {
+ const char *newline = strchr(text, '\n');
+ if(!newline)
+ return strlen(text);
+ else
+ return (int)(newline - text);
+ }
+
+The main function follows. In the beginning, we first declare a bunch
+of variables and check the command line parameters::
+
+ unsigned int i;
+ char *text;
+ char url[URL_SIZE];
+
+ json_t *root;
+ json_error_t error;
+ json_t *commits;
+
+ if(argc != 3)
+ {
+ fprintf(stderr, "usage: %s USER REPOSITORY\n\n", argv[0]);
+ fprintf(stderr, "List commits at USER's REPOSITORY.\n\n");
+ return 2;
+ }
+
+Then we build the request URL using the user and repository names
+given as command line parameters::
+
+ snprintf(url, URL_SIZE, URL_FORMAT, argv[1], argv[2]);
+
+This uses the ``URL_SIZE`` and ``URL_FORMAT`` constants defined above.
+Now we're ready to actually request the JSON data over the web::
+
+ text = request(url);
+ if(!text)
+ return 1;
+
+If an error occurs, our function ``request`` prints the error and
+returns *NULL*, so it's enough to just return 1 from the main
+function.
+
+Next we'll call :cfunc:`json_loads()` to decode the JSON text we got
+as a response::
+
+ root = json_loads(text, &error);
+ free(text);
+
+ if(!root)
+ {
+ fprintf(stderr, "error: on line %d: %s\n", error.line, error.text);
+ return 1;
+ }
+
+We don't need the JSON text anymore, so we can free the ``text``
+variable right after decoding it. If :cfunc:`json_loads()` fails, it
+returns *NULL* and sets error information to the :ctype:`json_error_t`
+structure given as the second parameter. In this case, our program
+prints the error information out and returns 1 from the main function.
+This check is really only to be sure, because we can assume that the
+GitHub API returns correct JSON to us.
+
+Next, we'll extract the ``commits`` array from the JSON response::
+
+ commits = json_object_get(root, "commits");
+ if(!commits || !json_is_array(commits))
+ {
+ fprintf(stderr, "error: commits is not an array\n");
+ return 1;
+ }
+
+This is the array that contains objects describing latest commits in
+the repository. If the key ``commits`` doesn't exist,
+:cfunc:`json_object_get()` returns *NULL*. We also check that the
+returned value really is an array.
+
+Then we proceed to loop over all the commits in the array::
+
+ for(i = 0; i < json_array_size(commits); i++)
+ {
+ json_t *commit, *id, *message;
+ const char *message_text;
+
+ commit = json_array_get(commits, i);
+ if(!json_is_object(commit))
+ {
+ fprintf(stderr, "error: commit %d is not an object\n", i + 1);
+ return 1;
+ }
+ ...
+
+The function :cfunc:`json_array_size()` returns the size of a JSON
+array. First, we again declare some variables and then extract the
+i'th element of the ``commits`` array using :cfunc:`json_array_get()`.
+We also check that the resulting value is a JSON object. (The
+structure of the response JSON was explained in
+:ref:`tutorial-github-commits-api`).
+
+Next we'll extract the commit ID and commit message, and check that
+they both are JSON strings::
+
+ id = json_object_get(commit, "id");
+ if(!id || !json_is_string(id))
+ {
+ fprintf(stderr, "error: commit %d: id is not a string\n", i + 1);
+ return 1;
+ }
+
+ message = json_object_get(commit, "message");
+ if(!message || !json_is_string(message))
+ {
+ fprintf(stderr, "error: commit %d: message is not a string\n", i + 1);
+ return 1;
+ }
+ ...
+
+And finally, we'll print the first 8 characters of the commit ID and
+the first line of the commit message. A C-style string is extracted
+from a JSON string using :cfunc:`json_string_value()`::
+
+ message_text = json_string_value(message);
+ printf("%.8s %.*s\n",
+ json_string_value(id),
+ newline_offset(message_text),
+ message_text);
+ }
+
+After sending the HTTP request, we decoded the JSON text using
+:cfunc:`json_loads()`, remember? It returns a *new reference* to a
+JSON value it decodes. When we're finished with the value, we'll need
+to decrease the reference count using :cfunc:`json_decref()`. This way
+Jansson can release the resources::
+
+ json_decref(root);
+ return 0;
+
+For a detailed explanation of reference counting in Jansson, see
+:ref:`apiref-reference-count` in :ref:`apiref`.
+
+The program's ready, let's test it and view the latest commits in
+Jansson's repository::
+
+ $ ./github_commits akheron jansson
+ 86dc1d62 Fix indentation
+ b67e130f json_dumpf: Document the output shortage on error
+ 4cd77771 Enhance handling of circular references
+ 79009e62 json_dumps: Close the strbuffer if dumping fails
+ 76999799 doc: Fix a small typo in apiref
+ 22af193a doc/Makefile.am: Remove *.pyc in clean
+ 951d091f Make integer, real and string mutable
+ 185e107d Don't use non-portable asprintf()
+ ca7703fb Merge branch '1.0'
+ 12cd4e8c jansson 1.0.4
+ <etc...>
+
+
+Conclusion
+==========
+
+In this tutorial, we implemented a program that fetches the latest
+commits of a GitHub repository using the GitHub commits API. Jansson
+was used to decode the JSON response and to extract the commit data.
+
+This tutorial only covered a small part of Jansson. For example, we
+did not create or manipulate JSON values at all. Proceed to
+:ref:`apiref` to explore all features of Jansson.
projects / profile / ivi / jansson.git / commitdiff