fastbootd: Add getvar max-fetch-size.

Test: run it
Test: see follow up CL on fuzzy_fastboot

Bug: 173654501

Change-Id: I5ed110c5569d83cbe791d04b4abea3a2af2765a9

fastboot/Android.bp

@@ -138,6 +138,12 @@ cc_binary {
 
     recovery: true,
 
+    product_variables: {
+        debuggable: {
+            cppflags: ["-DFB_ENABLE_FETCH"],
+        },
+    },
+
     srcs: [
         "device/commands.cpp",
         "device/fastboot_device.cpp",

fastboot/constants.h

@@ -77,3 +77,4 @@
 #define FB_VAR_FIRST_API_LEVEL "first-api-level"
 #define FB_VAR_SECURITY_PATCH_LEVEL "security-patch-level"
 #define FB_VAR_TREBLE_ENABLED "treble-enabled"
+#define FB_VAR_MAX_FETCH_SIZE "max-fetch-size"

fastboot/device/commands.cpp

@@ -136,7 +136,9 @@ bool GetVarHandler(FastbootDevice* device, const std::vector<std::string>& args)
             {FB_VAR_DYNAMIC_PARTITION, {GetDynamicPartition, nullptr}},
             {FB_VAR_FIRST_API_LEVEL, {GetFirstApiLevel, nullptr}},
             {FB_VAR_SECURITY_PATCH_LEVEL, {GetSecurityPatchLevel, nullptr}},
-            {FB_VAR_TREBLE_ENABLED, {GetTrebleEnabled, nullptr}}};
+            {FB_VAR_TREBLE_ENABLED, {GetTrebleEnabled, nullptr}},
+            {FB_VAR_MAX_FETCH_SIZE, {GetMaxFetchSize, nullptr}},
+    };
 
     if (args.size() < 2) {
         return device->WriteFail("Missing argument");

fastboot/device/commands.h

@@ -20,6 +20,7 @@
 #include <vector>
 
 constexpr unsigned int kMaxDownloadSizeDefault = 0x10000000;
+constexpr unsigned int kMaxFetchSizeDefault = 0x10000000;
 
 class FastbootDevice;
 

fastboot/device/variables.cpp

@@ -33,6 +33,12 @@
 #include "flashing.h"
 #include "utility.h"
 
+#ifdef FB_ENABLE_FETCH
+static constexpr bool kEnableFetch = true;
+#else
+static constexpr bool kEnableFetch = false;
+#endif
+
 using ::android::hardware::boot::V1_0::BoolResult;
 using ::android::hardware::boot::V1_0::Slot;
 using ::android::hardware::boot::V1_1::MergeStatus;
@@ -509,3 +515,13 @@ bool GetTrebleEnabled(FastbootDevice* /* device */, const std::vector<std::strin
     *message = android::base::GetProperty("ro.treble.enabled", "");
     return true;
 }
+
+bool GetMaxFetchSize(FastbootDevice* /* device */, const std::vector<std::string>& /* args */,
+                     std::string* message) {
+    if (!kEnableFetch) {
+        *message = "fetch not supported on user builds";
+        return false;
+    }
+    *message = android::base::StringPrintf("0x%X", kMaxFetchSizeDefault);
+    return true;
+}

fastboot/device/variables.h

@@ -80,6 +80,8 @@ bool GetSecurityPatchLevel(FastbootDevice* device, const std::vector<std::string
                            std::string* message);
 bool GetTrebleEnabled(FastbootDevice* device, const std::vector<std::string>& args,
                       std::string* message);
+bool GetMaxFetchSize(FastbootDevice* /* device */, const std::vector<std::string>& /* args */,
+                     std::string* message);
 
 // Helpers for getvar all.
 std::vector<std::vector<std::string>> GetAllPartitionArgsWithSlot(FastbootDevice* device);