feat(collector): add support for prometheus input client headers #3286
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📝 WalkthroughWalkthroughAdds optional custom HTTP headers support to the Prometheus Benthos input by introducing a headers map in config, propagating it through initialization, and wrapping the HTTP client with a custom RoundTripper to inject headers into all Prometheus API requests. Existing scraping and scheduling logic remains unchanged. Changes
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Actionable comments posted: 2
Caution
Some comments are outside the diff and can’t be posted inline due to platform limitations.
⚠️ Outside diff range comments (1)
collector/benthos/input/prometheus.go (1)
390-406: RoundTripper: add nil guards and ensure Header map exists.
Prevents panics if Header is nil and avoids NPE if next is unset.func (h *headerRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) { reqClone := req.Clone(req.Context()) + if reqClone.Header == nil { + reqClone.Header = make(http.Header) + } for key, value := range h.headers { reqClone.Header.Set(key, value) } - return h.next.RoundTrip(reqClone) + next := h.next + if next == nil { + next = http.DefaultTransport + } + return next.RoundTrip(reqClone) }I can add a small httptest validating header injection end-to-end.
🧹 Nitpick comments (2)
collector/benthos/input/prometheus.go (2)
65-67: Example: prefer env/secret over hardcoded credentials.
Use an env var in the example to discourage committing secrets.- headers: - Authorization: "Basic <base64 encoded credentials>" + headers: + Authorization: "Bearer ${PROMETHEUS_TOKEN}"
129-136: Header parsing LGTM; consider minimal validation.
Optionally warn on empty header keys/values to catch misconfigurations early.
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collector/benthos/input/prometheus.go(8 hunks)
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🔇 Additional comments (4)
collector/benthos/input/prometheus.go (4)
6-6: Import addition looks correct.
25-25: New config key constant is fine.
105-105: Struct field addition is appropriate.
214-214: Passing headers into the input is correct.
| service.NewStringMapField(fieldPrometheusHeaders). | ||
| Description("Optional HTTP headers to send with Prometheus queries. Useful for authentication or routing."). | ||
| Example(map[string]any{ | ||
| "Authorization": "Basic <base64 encoded credentials>", | ||
| }). | ||
| Optional(), | ||
| ).Example("Basic Configuration", "Collect Prometheus metrics with a scrape interval of 1 minute and a scrape offset of 30 seconds to account for delays in metric availability.", ` |
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💡 Verification agent
🧩 Analysis chain
Mark headers as sensitive to avoid leaking secrets.
If the Benthos service field API supports marking a map field as sensitive/redacted, please enable it; otherwise ensure configs aren’t logged verbatim and redact header values in any error messages.
🏁 Script executed:
#!/bin/bash
# Locate the constructor for StringMapField
rg -n "func NewStringMapField" -C3
# Inspect the StringMapField type for available methods
rg -n "type StringMapField" -C5
# Search for any sensitive/redaction support in the service package
rg -R "Sensitive" -n -C3 service
rg -R "Redact" -n -C3 serviceLength of output: 943
🏁 Script executed:
#!/bin/bash
# Identify the collector directory
find . -maxdepth 2 -type d -name collector
# Locate the prometheus.go file
find . -type f -iname "prometheus.go"
# Identify the service package directory
find . -maxdepth 2 -type d -name service
# Search for NewStringMapField usage
grep -R "NewStringMapField" -n .
# Search for any map-field types and methods in service package
grep -R "MapField" -n service
# Look for methods containing 'Sensitive' or 'Redact'
grep -RE "(Sensitive|Redact)" -n serviceLength of output: 462
🏁 Script executed:
#!/bin/bash
# Print the first 50 lines of go.mod to identify the Benthos service import path
sed -n '1,50p' go.modLength of output: 1844
🏁 Script executed:
#!/bin/bash
sed -n '1,50p' collector/benthos/input/prometheus.goLength of output: 1585
🌐 Web query:
pkg.go.dev github.com/benthosdev/benthos/v4/public/service NewStringMapField
💡 Result:
Signature:
func NewStringMapField(name string) *ConfigField
Description:
Defines a config field that is an object (map) of arbitrary keys with string values. Use ParsedConfig.FieldStringMap(...) to extract the map from a parsed config. [1]
Sources:
[1] pkg.go.dev — github.com/benthosdev/benthos/v4/public/service (NewStringMapField, FieldStringMap).
Add .Secret() to the headers field definition
The Benthos service API’s ConfigField supports a Secret() method—chain .Secret() on the service.NewStringMapField(fieldPrometheusHeaders) call in collector/benthos/input/prometheus.go to mark header values as sensitive and ensure they’re redacted in logs and errors. (pkg.go.dev)
🤖 Prompt for AI Agents
In collector/benthos/input/prometheus.go around lines 53 to 59, the Prometheus
headers field uses service.NewStringMapField(fieldPrometheusHeaders) but does
not mark values as secrets; chain the .Secret() method onto the
NewStringMapField call (i.e., service.NewStringMapField(...).Secret()...) so
header values are treated as sensitive and will be redacted in logs and errors,
leaving the rest of the field builder chain (Description, Example, Optional)
unchanged.
| // Create Prometheus client with custom headers | ||
| clientConfig := api.Config{ | ||
| Address: url, | ||
| }) | ||
| } | ||
|
|
||
| if len(headers) > 0 { | ||
| clientConfig.RoundTripper = &headerRoundTripper{ | ||
| next: api.DefaultRoundTripper, | ||
| headers: headers, | ||
| } | ||
| } | ||
|
|
||
| client, err := api.NewClient(clientConfig) | ||
| if err != nil { |
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🛠️ Refactor suggestion
Wrap RoundTripper defensively to allow future composition.
Use any pre-set RoundTripper as the next hop when present; fall back to the Prom client default.
- if len(headers) > 0 {
- clientConfig.RoundTripper = &headerRoundTripper{
- next: api.DefaultRoundTripper,
- headers: headers,
- }
- }
+ if len(headers) > 0 {
+ next := clientConfig.RoundTripper
+ if next == nil {
+ next = api.DefaultRoundTripper
+ }
+ clientConfig.RoundTripper = &headerRoundTripper{
+ next: next,
+ headers: headers,
+ }
+ }📝 Committable suggestion
‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.
| // Create Prometheus client with custom headers | |
| clientConfig := api.Config{ | |
| Address: url, | |
| }) | |
| } | |
| if len(headers) > 0 { | |
| clientConfig.RoundTripper = &headerRoundTripper{ | |
| next: api.DefaultRoundTripper, | |
| headers: headers, | |
| } | |
| } | |
| client, err := api.NewClient(clientConfig) | |
| if err != nil { | |
| // Create Prometheus client with custom headers | |
| clientConfig := api.Config{ | |
| Address: url, | |
| } | |
| if len(headers) > 0 { | |
| next := clientConfig.RoundTripper | |
| if next == nil { | |
| next = api.DefaultRoundTripper | |
| } | |
| clientConfig.RoundTripper = &headerRoundTripper{ | |
| next: next, | |
| headers: headers, | |
| } | |
| } | |
| client, err := api.NewClient(clientConfig) | |
| if err != nil { | |
| // ... | |
| } |
🤖 Prompt for AI Agents
In collector/benthos/input/prometheus.go around lines 184 to 197, the
headerRoundTripper is currently hard-coded to wrap api.DefaultRoundTripper;
instead, detect any existing clientConfig.RoundTripper and use it as the next
hop (falling back to api.DefaultRoundTripper if nil) so future composition
works. Change the construction to pick next := clientConfig.RoundTripper; if
next == nil { next = api.DefaultRoundTripper } and pass that next into
headerRoundTripper, leaving the headers logic unchanged.
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