Make serd_strtod API const-correct

This is an API breakage, but a minor one (particularly since NULL is
allowed) that avoids the flaw in the C API.

7 files changed, 16 insertions, 11 deletions

diff --git a/NEWS b/NEWS
index a503eaee..72deca90 100644
--- a/NEWS
+++ b/NEWS
@@ -4,6 +4,7 @@ serd (1.0.0) unstable;
   * Remove useless character counting from API
   * Use char* for strings in public API
   * Rename SerdChunk to SerdStringView
+  * Make serd_strtod API const-correct
 
  -- David Robillard <d@drobilla.net>  Sat, 19 Jan 2019 13:31:12 +0100
 
diff --git a/serd/serd.h b/serd/serd.h
index e8aff1e8..ba285255 100644
--- a/serd/serd.h
+++ b/serd/serd.h
@@ -316,13 +316,15 @@ serd_strlen(const char* str, SerdNodeFlags* flags);
 /**
    Parse a string to a double.
 
-   The API of this function is identical to the standard C strtod function,
+   The API of this function is similar to the standard C strtod function,
    except this function is locale-independent and always matches the lexical
-   format used in the Turtle grammar (the decimal point is always ".").
+   format used in the Turtle grammar (the decimal point is always ".").  The
+   end parameter is an offset from the start of `str` to avoid the
+   const-correctness issues of the strtod API.
 */
 SERD_API
 double
-serd_strtod(const char* str, char** endptr);
+serd_strtod(const char* str, size_t* end);
 
 /**
    Decode a base64 string.
diff --git a/src/reader.c b/src/reader.c
index 0eb06c88..37c4719c 100644
--- a/src/reader.c
+++ b/src/reader.c
@@ -79,7 +79,7 @@ Ref
 push_node_padded(SerdReader* reader, size_t maxlen,
                  SerdType type, const char* str, size_t n_bytes)
 {
-	char* mem = (char*)serd_stack_push_aligned(
+	void* mem = serd_stack_push_aligned(
 		&reader->stack, sizeof(SerdNode) + maxlen + 1, sizeof(SerdNode));
 
 	SerdNode* const node = (SerdNode*)mem;
diff --git a/src/reader.h b/src/reader.h
index 6e1a24d7..f3ddde0a 100644
--- a/src/reader.h
+++ b/src/reader.h
@@ -68,7 +68,7 @@ static inline SerdStatus
 push_byte(SerdReader* reader, Ref ref, const uint8_t c)
 {
 	SERD_STACK_ASSERT_TOP(reader, ref);
-	char* const     s    = serd_stack_push(&reader->stack, 1);
+	char* const     s    = (char*)serd_stack_push(&reader->stack, 1);
 	SerdNode* const node = (SerdNode*)(reader->stack.buf + ref);
 	++node->n_bytes;
 	*(s - 1) = c;
diff --git a/src/serd_internal.h b/src/serd_internal.h
index c51b88ed..62c0a72c 100644
--- a/src/serd_internal.h
+++ b/src/serd_internal.h
@@ -195,7 +195,7 @@ serd_stack_free(SerdStack* stack)
 	stack->size     = 0;
 }
 
-static inline char*
+static inline void*
 serd_stack_push(SerdStack* stack, size_t n_bytes)
 {
 	const size_t new_size = stack->size + n_bytes;
diff --git a/src/string.c b/src/string.c
index a1d46507..01ed25a0 100644
--- a/src/string.c
+++ b/src/string.c
@@ -100,7 +100,7 @@ read_sign(const char** sptr)
 }
 
 double
-serd_strtod(const char* str, char** endptr)
+serd_strtod(const char* str, size_t* end)
 {
 	double result = 0.0;
 
@@ -136,8 +136,8 @@ serd_strtod(const char* str, char** endptr)
 		result *= pow(10, expt * expt_sign);
 	}
 
-	if (endptr) {
-		*endptr = (char*)s;
+	if (end) {
+		*end = s - str;
 	}
 
 	return result * sign;
diff --git a/tests/serd_test.c b/tests/serd_test.c
index c2d70136..6f041e2d 100644
--- a/tests/serd_test.c
+++ b/tests/serd_test.c
@@ -39,11 +39,13 @@ test_strtod(double dbl, double max_delta)
 	char buf[1024];
 	snprintf(buf, sizeof(buf), "%f", dbl);
 
-	char* endptr = NULL;
-	const double out = serd_strtod(buf, &endptr);
+	size_t       end = 0;
+	const double out = serd_strtod(buf, &end);
 
 	const double diff = fabs(out - dbl);
 	assert(diff <= max_delta);
+	assert(end == strlen(buf));
+
 	return 0;
 }