Add a function to validate a WebPDecoderConfig

This echoes WebPValidateConfig for encoding.

Change-Id: Ib404d55c7af4d0755644879ec491e3998e6b5e8d

src/dec/buffer_dec.c

@@ -26,10 +26,9 @@ static const uint8_t kModeBpp[MODE_LAST] = {
   4, 4, 4, 2,    // pre-multiplied modes
   1, 1 };
 
-// Check that webp_csp_mode is within the bounds of WEBP_CSP_MODE.
 // Convert to an integer to handle both the unsigned/signed enum cases
 // without the need for casting to remove type limit warnings.
-static int IsValidColorspace(int webp_csp_mode) {
+int IsValidColorspace(int webp_csp_mode) {
   return (webp_csp_mode >= MODE_RGB && webp_csp_mode < MODE_LAST);
 }
 

src/dec/common_dec.h

@@ -51,4 +51,7 @@ enum { MB_FEATURE_TREE_PROBS = 3,
        NUM_PROBAS = 11
      };
 
+// Check that webp_csp_mode is within the bounds of WEBP_CSP_MODE.
+int IsValidColorspace(int webp_csp_mode);
+
 #endif  // WEBP_DEC_COMMON_DEC_H_

src/dec/webp_dec.c

@@ -13,13 +13,15 @@
 
 #include <stdlib.h>
 
+#include "src/dec/common_dec.h"
 #include "src/dec/vp8_dec.h"
 #include "src/dec/vp8i_dec.h"
 #include "src/dec/vp8li_dec.h"
 #include "src/dec/webpi_dec.h"
+#include "src/utils/rescaler_utils.h"
 #include "src/utils/utils.h"
-#include "src/webp/mux_types.h"  // ALPHA_FLAG
 #include "src/webp/decode.h"
+#include "src/webp/mux_types.h"  // ALPHA_FLAG
 #include "src/webp/types.h"
 
 //------------------------------------------------------------------------------
@@ -747,6 +749,61 @@ int WebPInitDecoderConfigInternal(WebPDecoderConfig* config,
   return 1;
 }
 
+static int WebPCheckCropDimensionsBasic(int x, int y, int w, int h) {
+  return !(x < 0 || y < 0 || w <= 0 || h <= 0);
+}
+
+int WebPValidateDecoderConfig(const WebPDecoderConfig* config) {
+  const WebPDecoderOptions* options;
+  if (config == NULL) return 0;
+  if (!IsValidColorspace(config->output.colorspace)) {
+    return 0;
+  }
+
+  options = &config->options;
+  // bypass_filtering, no_fancy_upsampling, use_cropping, use_scaling,
+  // use_threads, flip can be any integer and are interpreted as boolean.
+
+  // Check for cropping.
+  if (options->use_cropping && !WebPCheckCropDimensionsBasic(
+                                   options->crop_left, options->crop_top,
+                                   options->crop_width, options->crop_height)) {
+    return 0;
+  }
+  // Check for scaling.
+  if (options->use_scaling &&
+      (options->scaled_width < 0 || options->scaled_height < 0 ||
+       (options->scaled_width == 0 && options->scaled_height == 0))) {
+    return 0;
+  }
+
+  // In case the WebPBitstreamFeatures has been filled in, check further.
+  if (config->input.width > 0 || config->input.height > 0) {
+    int scaled_width = options->scaled_width;
+    int scaled_height = options->scaled_height;
+    if (options->use_cropping &&
+        !WebPCheckCropDimensions(config->input.width, config->input.height,
+                                 options->crop_left, options->crop_top,
+                                 options->crop_width, options->crop_height)) {
+      return 0;
+    }
+    if (options->use_scaling && !WebPRescalerGetScaledDimensions(
+                                    config->input.width, config->input.height,
+                                    &scaled_width, &scaled_height)) {
+      return 0;
+    }
+  }
+
+  // Check for dithering.
+  if (options->dithering_strength < 0 || options->dithering_strength > 100 ||
+      options->alpha_dithering_strength < 0 ||
+      options->alpha_dithering_strength > 100) {
+    return 0;
+  }
+
+  return 1;
+}
+
 VP8StatusCode WebPGetFeaturesInternal(const uint8_t* data, size_t data_size,
                                       WebPBitstreamFeatures* features,
                                       int version) {
@@ -806,8 +863,8 @@ VP8StatusCode WebPDecode(const uint8_t* data, size_t data_size,
 
 int WebPCheckCropDimensions(int image_width, int image_height,
                             int x, int y, int w, int h) {
-  return !(x < 0 || y < 0 || w <= 0 || h <= 0 ||
-           x >= image_width || w > image_width || w > image_width - x ||
+  return WebPCheckCropDimensionsBasic(x, y, w, h) &&
+         !(x >= image_width || w > image_width || w > image_width - x ||
            y >= image_height || h > image_height || h > image_height - y);
 }
 

src/webp/decode.h

@@ -20,7 +20,7 @@
 extern "C" {
 #endif
 
-#define WEBP_DECODER_ABI_VERSION 0x0209    // MAJOR(8b) + MINOR(8b)
+#define WEBP_DECODER_ABI_VERSION 0x0210    // MAJOR(8b) + MINOR(8b)
 
 // Note: forward declaring enumerations is not allowed in (strict) C and C++,
 // the types are left here for reference.
@@ -451,7 +451,9 @@ struct WebPDecoderOptions {
                                       // Will be snapped to even values.
   int crop_width, crop_height;        // dimension of the cropping area
   int use_scaling;                    // if true, scaling is applied _afterward_
-  int scaled_width, scaled_height;    // final resolution
+  int scaled_width, scaled_height;    // final resolution. if one is 0, it is
+                                      // guessed from the other one to keep the
+                                      // original ratio.
   int use_threads;                    // if true, use multi-threaded decoding
   int dithering_strength;             // dithering strength (0=Off, 100=full)
   int flip;                           // if true, flip output vertically
@@ -479,6 +481,11 @@ WEBP_NODISCARD static WEBP_INLINE int WebPInitDecoderConfig(
   return WebPInitDecoderConfigInternal(config, WEBP_DECODER_ABI_VERSION);
 }
 
+// Returns true if 'config' is non-NULL and all configuration parameters are
+// within their valid ranges.
+WEBP_NODISCARD WEBP_EXTERN int WebPValidateDecoderConfig(
+    const WebPDecoderConfig* config);
+
 // Instantiate a new incremental decoder object with the requested
 // configuration. The bitstream can be passed using 'data' and 'data_size'
 // parameter, in which case the features will be parsed and stored into