feat(www): add cheat-sheet.

1 files changed, 71 insertions, 9 deletions

diff --git a/www/content/posts/c-func-ext.md b/www/content/posts/c-func-ext.md
index f5ab8fb..f0fce10 100644
--- a/www/content/posts/c-func-ext.md
+++ b/www/content/posts/c-func-ext.md
@@ -8,16 +8,78 @@ tags:
   - posix
 ---
 
-Recently, I've been working on porting libraries to GNU/Hurd. The maintainers of GNU/Hurd
-have a strong belief that [`*_MAX` macros on POSIX system interfaces](https://pubs.opengroup.org/onlinepubs/9699919799.2008edition/nframe.html)
-are very evil things. This is indeed true as a lot of (old) libraries relying on those macros
-to determine the buffer size. In modern programming world, it is definitely a bad
-idea to use fixed values for buffer sizes without considering possible overflow, unless
-you are certain that size is sufficient.
-
-When you get rid of some old things, you will always meet compatibility problems. In these
-case, old source codes using these macros just do not compile now. So here are some
+Recently, I’ve been working on porting some libraries to GNU/Hurd. Many (old)
+libraries use [`*_MAX` constants on POSIX system
+interfaces](https://pubs.opengroup.org/onlinepubs/9699919799.2008edition/nframe.html)
+to calculate buffer sizes. However, the GNU/Hurd maintainers urge against the
+blind use of them and refuse to define them in system headers. When old APIs are
+gone, compatibility problems come. To make my life easier, I'll put some
+reusable code snippets here to help *fix `*_MAX` bugs*.
 
 <!--more-->
 
+```c
+#include <errno.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+static inline char *xreadlink(const char *restrict path) {
+  char *buffer;
+  size_t allocated = 128;
+  ssize_t len;
+
+  while (1) {
+    buffer = (char *)malloc(allocated);
+    if (!buffer) {
+      return NULL;
+    }
+    len = readlink(path, buffer, allocated);
+    if (len < (ssize_t)allocated) {
+      return buffer;
+    }
+    free(buffer);
+    if (len >= (ssize_t)allocated) {
+      allocated *= 2;
+      continue;
+    }
+    return NULL;
+  }
+}
+
+static inline char *xgethostname() {
+  long max_host_name;
+  char *buffer;
+
+  max_host_name = sysconf(_SC_HOST_NAME_MAX);
+  buffer = malloc(max_host_name + 1);
+
+  if (gethostname(buffer, max_host_name + 1)) {
+    free(buffer);
+    return NULL;
+  }
+
+  buffer[max_host_name] = '\0';
+  return buffer;
+}
+
+static inline char *xgetcwd() {
+  char *buffer;
+  size_t allocated = 128;
 
+  while (1) {
+    buffer = (char *)malloc(allocated);
+    if (!buffer) {
+      return NULL;
+    }
+    getcwd(buffer, allocated);
+    if (buffer)
+      return buffer;
+    free(buffer);
+    if (errno == ERANGE) {
+      allocated *= 2;
+      continue;
+    }
+    return NULL;
+  }
+}
+```