1 files changed, 42 insertions, 5 deletions

diff --git a/src/core/compression/compression_algorithm.c b/src/core/compression/compression_algorithm.c
index 6f3a8eb28e..2810a38b68 100644
--- a/src/core/compression/compression_algorithm.c
+++ b/src/core/compression/compression_algorithm.c
@@ -128,20 +128,57 @@ grpc_mdelem *grpc_compression_encoding_mdelem(
 /* TODO(dgq): Add the ability to specify parameters to the individual
  * compression algorithms */
 grpc_compression_algorithm grpc_compression_algorithm_for_level(
-    grpc_compression_level level) {
+    grpc_compression_level level, uint32_t accepted_encodings) {
   GRPC_API_TRACE("grpc_compression_algorithm_for_level(level=%d)", 1,
                  ((int)level));
+  if (level > GRPC_COMPRESS_LEVEL_HIGH) {
+    gpr_log(GPR_ERROR, "Unknown compression level %d.", (int)level);
+    abort();
+  }
+
+  const size_t num_supported =
+      GPR_BITCOUNT(accepted_encodings) - 1; /* discard NONE */
+  if (level == GRPC_COMPRESS_LEVEL_NONE || num_supported == 0) {
+    return GRPC_COMPRESS_NONE;
+  }
+
+  GPR_ASSERT(level > 0);
+
+  /* Establish a "ranking" or compression algorithms in increasing order of
+   * compression.
+   * This is simplistic and we will probably want to introduce other dimensions
+   * in the future (cpu/memory cost, etc). */
+  const grpc_compression_algorithm algos_ranking[] = {GRPC_COMPRESS_GZIP,
+                                                      GRPC_COMPRESS_DEFLATE};
+
+  /* intersect algos_ranking with the supported ones keeping the ranked order */
+  grpc_compression_algorithm
+      sorted_supported_algos[GRPC_COMPRESS_ALGORITHMS_COUNT];
+  size_t algos_supported_idx = 0;
+  for (size_t i = 0; i < GPR_ARRAY_SIZE(algos_ranking); i++) {
+    const grpc_compression_algorithm alg = algos_ranking[i];
+    for (size_t j = 0; j < num_supported; j++) {
+      if (GPR_BITGET(accepted_encodings, alg) == 1) {
+        /* if \a alg in supported */
+        sorted_supported_algos[algos_supported_idx++] = alg;
+        break;
+      }
+    }
+    if (algos_supported_idx == num_supported) break;
+  }
+
   switch (level) {
     case GRPC_COMPRESS_LEVEL_NONE:
-      return GRPC_COMPRESS_NONE;
+      abort(); /* should have been handled already */
     case GRPC_COMPRESS_LEVEL_LOW:
+      return sorted_supported_algos[0];
     case GRPC_COMPRESS_LEVEL_MED:
+      return sorted_supported_algos[num_supported / 2];
     case GRPC_COMPRESS_LEVEL_HIGH:
-      return GRPC_COMPRESS_DEFLATE;
+      return sorted_supported_algos[num_supported - 1];
     default:
-      gpr_log(GPR_ERROR, "Unknown compression level %d.", (int)level);
       abort();
-  }
+  };
 }
 
 void grpc_compression_options_init(grpc_compression_options *opts) {