[receiver/haproxy] fix reading more than 4096 bytes (open-telemetry#3…

…2661)

This makes sure to read the whole data when interacting over the socket
with haproxy.

Fixes open-telemetry#32652

.chloggen/haproxy_readall.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: haproxyreceiver
+
+# A brief description of the change. Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix reading stats larger than 4096 bytes
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [32652]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

receiver/haproxyreceiver/scraper.go

@@ -70,12 +70,10 @@ func (s *scraper) scrape(ctx context.Context) (pmetric.Metrics, error) {
  if err != nil {
  return pmetric.NewMetrics(), err
  }
- buf := make([]byte, 4096)
- n, err := c.Read(buf)
+ buf, err := io.ReadAll(c)
  if err != nil {
  return pmetric.NewMetrics(), err
  }
- buf = buf[0:n]
  records, err = s.readStats(buf)
  if err != nil {
  return pmetric.NewMetrics(), fmt.Errorf("error reading stats: %w", err)

receiver/haproxyreceiver/scraper_test.go

@@ -41,6 +41,7 @@ func Test_scraper_readStats(t *testing.T) {
  require.NoError(t, err2)
  _, err2 = c.Write(stats)
  require.NoError(t, err2)
+ require.NoError(t, c.Close())
  default:
  require.Fail(t, fmt.Sprintf("invalid message: %v", data))
  }