fix(mmds): Update micro-http for empty MMDS path

When querying a MMDS path that has an empty content, the response didn't
contain 'Content-Length' field, resulting in the client waiting for the
connection closed by the server or timeout. To fix this issue,
micro-http made a change to have the field when the response status code
is not 1XX or 204. This commit updates Cargo.lock file to consume this
change and also adds an integration test to ensure that it doesn't
timeout for an empty MMDS path.

The micro-http's change was made on
firecracker-microvm/micro-http#48.

Signed-off-by: Takahiro Itazuri <[email protected]>

Author: zulinx86

CHANGELOG.md

@@ -74,6 +74,10 @@ and this project adheres to
   mechanism to reliably fetch Firecracker PID. With this change, Firecracker
   process's PID will always be available in the Jailer's root directory
   regardless of whether new_pid_ns was set.
+- [#4468](https://github.com/firecracker-microvm/firecracker/pull/4468): Fixed a
+  bug where a client would hang or timeout when querying for an MMDS path whose
+  content is empty, because the 'Content-Length' header field was missing in a
+  response.
 
 ## \[1.6.0\]
 

Cargo.lock

@@ -296,6 +296,7 @@ def test_mmds_response(uvm_plain, version):
                     "res_key": "res_value",
                 },
                 "dummy_array": ["arr_val1", "arr_val2"],
+                "dummy_empty": "",
             },
             "Limits": {"CPU": 512, "Memory": 512},
             "Usage": {"CPU": 12.12},
@@ -328,12 +329,12 @@ def test_mmds_response(uvm_plain, version):
     expected = (
         "ami-id\n"
         "dummy_array\n"
+        "dummy_empty\n"
         "dummy_obj/\n"
         "local-hostname\n"
         "public-hostname\n"
         "reservation-id"
     )
-
     run_guest_cmd(ssh_connection, cmd, expected)
 
     cmd = pre + "latest/meta-data/ami-id/"
@@ -342,6 +343,9 @@ def test_mmds_response(uvm_plain, version):
     cmd = pre + "latest/meta-data/dummy_array/0"
     run_guest_cmd(ssh_connection, cmd, "arr_val1")
 
+    cmd = pre + "latest/meta-data/dummy_empty"
+    run_guest_cmd(ssh_connection, cmd, "")
+
     cmd = pre + "latest/Usage/CPU"
     run_guest_cmd(
         ssh_connection,