fastboot driver: add fetch command in driver

The `fastboot fetch` command is a wrapper around
the fetch protocol. It:

- getvar max-fetch-size
- get the size of the partition
- read the data by chunks, chunk size = max-fetch-size.

The name of the partition is passed directly to the device
(with the usual has-slot magic for flashing etc.) If we support
fetching partitions other than vendor_boot in the future, no change
in the driver is needed.

Bug: 173654501
Test: manual

Change-Id: Ie576eea668234df236b096a372e65c5e91c1e48c

1 files changed, 25 insertions, 0 deletions

diff --git a/fastboot/fastboot_driver.cpp b/fastboot/fastboot_driver.cpp
index a516a9130..14ee78555 100644
--- a/fastboot/fastboot_driver.cpp
+++ b/fastboot/fastboot_driver.cpp
@@ -30,6 +30,7 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#include <inttypes.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -42,6 +43,7 @@
 
 #include <android-base/file.h>
 #include <android-base/mapped_file.h>
+#include <android-base/parseint.h>
 #include <android-base/stringprintf.h>
 #include <android-base/strings.h>
 #include <android-base/unique_fd.h>
@@ -357,6 +359,29 @@ RetCode FastBootDriver::UploadInner(const std::string& outfile, std::string* res
     return ret;
 }
 
+RetCode FastBootDriver::FetchToFd(const std::string& partition, android::base::borrowed_fd fd,
+                                  int64_t offset, int64_t size, std::string* response,
+                                  std::vector<std::string>* info) {
+    prolog_(android::base::StringPrintf("Fetching %s (offset=%" PRIx64 ", size=%" PRIx64 ")",
+                                        partition.c_str(), offset, size));
+    std::string cmd = FB_CMD_FETCH ":" + partition;
+    if (offset >= 0) {
+        cmd += android::base::StringPrintf(":0x%08" PRIx64, offset);
+        if (size >= 0) {
+            cmd += android::base::StringPrintf(":0x%08" PRIx64, size);
+        }
+    }
+    RetCode ret = RunAndReadBuffer(cmd, response, info, [&](const char* data, uint64_t size) {
+        if (!android::base::WriteFully(fd, data, size)) {
+            error_ = android::base::StringPrintf("Cannot write: %s", strerror(errno));
+            return IO_ERROR;
+        }
+        return SUCCESS;
+    });
+    epilog_(ret);
+    return ret;
+}
+
 // Helpers
 void FastBootDriver::SetInfoCallback(std::function<void(const std::string&)> info) {
     info_ = info;