fix(httpcheckreceiver): always close resp.Body (#40552)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

The Go HTTP client documentation specifically states that when an error
occurs, the response may still be non-nil, and you're responsible for
closing the body to avoid resource leaks. And added a sensible timeout
to prevent the connection hang indefinitely.

<!-- Issue number (e.g. #1234) or full URL to issue, if applicable. -->
#### Link to tracking issue
Fixes

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#### Testing

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#### Documentation

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Author: srikanthccv

.chloggen/always_close_resp_body_and_add_timeout.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: breaking
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: receiver/httpcheck
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Always close resp.Body and add timeout
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [40552]
+
+# (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/httpcheckreceiver/scraper.go

@@ -6,6 +6,7 @@ package httpcheckreceiver // import "github.com/open-telemetry/opentelemetry-col
 import (
 	"context"
 	"errors"
+	"io"
 	"net/http"
 	"sync"
 	"time"
@@ -37,6 +38,11 @@ func (h *httpcheckScraper) start(ctx context.Context, host component.Host) (err
 	var expandedTargets []*targetConfig
 
 	for _, target := range h.cfg.Targets {
+		if target.Timeout == 0 {
+			// Set a reasonable timeout to prevent hanging requests
+			target.Timeout = 30 * time.Second
+		}
+
 		// Create a unified list of endpoints
 		var allEndpoints []string
 		if len(target.Endpoints) > 0 {
@@ -103,8 +109,16 @@ func (h *httpcheckScraper) scrape(ctx context.Context) (pmetric.Metrics, error)
 			// Send the request and measure response time
 			start := time.Now()
 			resp, err := targetClient.Do(req)
-			if err == nil {
-				defer resp.Body.Close()
+
+			// Always close response body if it exists, even on error
+			if resp != nil && resp.Body != nil {
+				defer func() {
+					// Drain the body to allow connection reuse
+					_, _ = io.Copy(io.Discard, resp.Body)
+					if closeErr := resp.Body.Close(); closeErr != nil {
+						h.settings.Logger.Error("failed to close response body", zap.Error(closeErr))
+					}
+				}()
 			}
 
 			mux.Lock()