util: Add a string buffer implementation

Based on Vladislav Egorovs work on the preprocessor, but split
out to a util functionality that should be universal. Setup, teardown,
memory handling and general layout is modeled around the hash_table
and the set, to make it familiar for everyone.

A notable change is that this implementation is always null terminated.
The rationale is that it will be less error-prone, as one might
access the buffer directly, thereby reading a non-terminated string.
Also, vsnprintf and friends prints the null-terminator.

Signed-off-by: Thomas Helland <thomashelland90@gmail.com>
Tested-by: Dieter Nützel <Dieter at nuetzel-hh.de>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

V2: Address review feedback from Timothy and Grazvydas
   - Fix MINGW preprocessor check
   - Changed len from uint to int
   - Make string argument const in append function
   - Move to header and inline append function
   - Add crimp_to_fit function for resizing buffer

V3: Move include of ralloc to string_buffer.h

V4: Use u_string.h for a cross-platform working vsnprintf

V5: Remember to cast to char * in crimp function

V6: Address review feedback from Nicolai
   - Handle !str->buf in buffer_create
   - Ensure va_end is always called in buffer_append_all
   - Add overflow check in buffer_append_len
   - Do not expose buffer_space_left, just remove it
   - Clarify why a loop is used in vprintf, change to for-loop
   - Add a va_copy to buffer_vprintf to fix failure to append arguments
     when having to resize the buffer for vsnprintf.

V7: Address more review feedback from Nicolai
   - Add missing va_end corresponding to va_copy
   - Error check failure to allocate in crimp_to_fit

src/util/string_buffer.c

@@ -0,0 +1,148 @@
+/*
+ * Copyright © 2017 Thomas Helland
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ */
+
+#include "string_buffer.h"
+
+static bool
+ensure_capacity(struct _mesa_string_buffer *str, uint32_t needed_capacity)
+{
+   if (needed_capacity <= str->capacity)
+      return true;
+
+   /* Too small, double until we can fit the new string */
+   uint32_t new_capacity = str->capacity * 2;
+   while (needed_capacity > new_capacity)
+      new_capacity *= 2;
+
+   str->buf = reralloc_array_size(str, str->buf, sizeof(char), new_capacity);
+   if (str->buf == NULL)
+      return false;
+
+   str->capacity = new_capacity;
+   return true;
+}
+
+struct _mesa_string_buffer *
+_mesa_string_buffer_create(void *mem_ctx, uint32_t initial_capacity)
+{
+   struct _mesa_string_buffer *str;
+   str = ralloc(mem_ctx, struct _mesa_string_buffer);
+
+   if (str == NULL)
+      return NULL;
+
+   /* If no initial capacity is set then set it to something */
+   str->capacity = initial_capacity ? initial_capacity : 32;
+   str->buf = ralloc_array(str, char, str->capacity);
+
+   if (!str->buf) {
+      ralloc_free(str);
+      return NULL;
+   }
+
+   str->length = 0;
+   str->buf[str->length] = '\0';
+   return str;
+}
+
+bool
+_mesa_string_buffer_append_all(struct _mesa_string_buffer *str,
+                               uint32_t num_args, ...)
+{
+   int i;
+   char* s;
+   va_list args;
+   va_start(args, num_args);
+   for (i = 0; i < num_args; i++) {
+      s = va_arg(args, char*);
+      if (!_mesa_string_buffer_append_len(str, s, strlen(s))) {
+         va_end(args);
+         return false;
+      }
+   }
+   va_end(args);
+   return true;
+}
+
+bool
+_mesa_string_buffer_append_len(struct _mesa_string_buffer *str,
+                               const char *c, uint32_t len)
+{
+   uint32_t needed_length = str->length + len + 1;
+
+   /* Check if we're overflowing uint32_t */
+   if (needed_length < str->length)
+      return false;
+
+   if (!ensure_capacity(str, needed_length))
+      return false;
+
+   memcpy(str->buf + str->length, c, len);
+   str->length += len;
+   str->buf[str->length] = '\0';
+   return true;
+}
+
+bool
+_mesa_string_buffer_vprintf(struct _mesa_string_buffer *str,
+                            const char *format, va_list args)
+{
+   /* We're looping two times to avoid duplicating code */
+   for (uint32_t i = 0; i < 2; i++) {
+      va_list arg_copy;
+      va_copy(arg_copy, args);
+      uint32_t space_left = str->capacity - str->length;
+
+      int32_t len = util_vsnprintf(str->buf + str->length,
+                                   space_left, format, arg_copy);
+      va_end(arg_copy);
+
+      /* Error in vsnprintf() or measured len overflows size_t */
+      if (unlikely(len < 0 || str->length + len + 1 < str->length))
+         return false;
+
+      /* There was enough space for the string; we're done */
+      if (len < space_left) {
+         str->length += len;
+         return true;
+      }
+
+      /* Not enough space, resize and retry */
+      ensure_capacity(str, str->length + len + 1);
+   }
+
+   return false;
+}
+
+bool
+_mesa_string_buffer_printf(struct _mesa_string_buffer *str,
+                            const char *format, ...)
+{
+   bool res;
+   va_list args;
+   va_start(args, format);
+   res = _mesa_string_buffer_vprintf(str, format, args);
+   va_end(args);
+   return res;
+}