fix(inputs.gnmi): Refactor alias handling

Rather than abritrarily take the substring of key, ensure that the key
contains the alias in the first place, then do the removal. Otherwise,
always take the base path.

fixes: #14530

plugins/inputs/gnmi/handler.go

@@ -7,7 +7,6 @@ import (
 	"fmt"
 	"io"
 	"net"
-	"path"
 	"sort"
 	"strconv"
 	"strings"
@@ -231,30 +230,33 @@ func (h *handler) handleSubscribeResponseUpdate(acc telegraf.Accumulator, respon
 				h.emptyNameWarnShown = true
 			}
 		}
+		aliasInfo := newInfoFromString(aliasPath)
 
 		// Group metrics
-		fieldPath := field.path.String()
-		key := strings.ReplaceAll(fieldPath, "-", "_")
+		var key string
 		if h.canonicalFieldNames {
 			// Strip the origin is any for the field names
-			if parts := strings.SplitN(key, ":", 2); len(parts) == 2 {
+			if parts := strings.SplitN(strings.ReplaceAll(field.path.String(), "-", "_"), ":", 2); len(parts) == 2 {
 				key = parts[1]
 			}
 		} else {
-			if len(aliasPath) < len(key) && len(aliasPath) != 0 {
-				// This may not be an exact prefix, due to naming style
-				// conversion on the key.
-				key = key[len(aliasPath)+1:]
-			} else if len(aliasPath) >= len(key) {
+			// If the origis are the same and the alias is shorter than the
+			// full path to avoid an empty key, then strip the common part if
+			// the field is prefixed with the alias path.
+			if aliasInfo.origin == field.path.origin && aliasInfo.isSubPathOf(field.path) && len(aliasInfo.segments) < len(field.path.segments) {
+				relative := field.path.segments[len(aliasInfo.segments):len(field.path.segments)]
+				key = strings.Join(relative, "/")
+			} else {
 				// Otherwise use the last path element as the field key.
-				key = path.Base(key)
+				key = field.path.segments[len(field.path.segments)-1]
 			}
+			key = strings.ReplaceAll(key, "-", "_")
 		}
 		if h.trimSlash {
 			key = strings.TrimLeft(key, "/.")
 		}
 		if key == "" {
-			h.log.Errorf("Invalid empty path %q with alias %q", fieldPath, aliasPath)
+			h.log.Errorf("Invalid empty path %q with alias %q", field.path.String(), aliasPath)
 			continue
 		}
 		grouper.Add(name, tags, timestamp, key, field.value)

plugins/inputs/gnmi/path.go

@@ -187,6 +187,11 @@ func (pi *pathInfo) normalize() {
 	if len(groups) == 2 {
 		pi.origin = groups[1]
 		pi.segments[0] = pi.segments[0][len(groups[1])+1:]
+
+		// if we get empty string back, remove the segment
+		if pi.segments[0] == "" {
+			pi.segments = pi.segments[1:]
+		}
 	}
 }
 

plugins/inputs/gnmi/testcases/issue_14530/expected.out

@@ -0,0 +1 @@
+ifcounters,name=Ethernet35,path=/interfaces/interface/state/counters,source=127.0.0.1 in_broadcast_pkts=0u,in_discards=0u,in_errors=0u,in_fcs_errors=0u,in_multicast_pkts=0u,in_octets=0u,in_pkts=0u,in_unicast_pkts=0u,out_broadcast_pkts=0u,out_discards=0u,out_errors=0u,out_multicast_pkts=0u,out_octets=0u,out_pkts=0u,out_unicast_pkts=0u 1704442117721474264

plugins/inputs/gnmi/testcases/issue_14530/responses.json

@@ -0,0 +1,208 @@
+[
+  {
+    "update": {
+      "timestamp": "1704442117721474264",
+      "prefix": {
+        "elem": [
+          {
+            "name": "interfaces"
+          },
+          {
+            "name": "interface",
+            "key": {
+              "name": "Ethernet35"
+            }
+          },
+          {
+            "name": "state"
+          },
+          {
+            "name": "counters"
+          }
+        ]
+      },
+      "update": [
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "in-broadcast-pkts"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "in-discards"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "in-errors"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "in-fcs-errors"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "in-multicast-pkts"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "in-octets"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "in-pkts"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "in-unicast-pkts"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "out-broadcast-pkts"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "out-discards"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "out-errors"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "out-multicast-pkts"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "out-octets"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "out-pkts"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        },
+        {
+          "path": {
+            "elem": [
+              {
+                "name": "out-unicast-pkts"
+              }
+            ]
+          },
+          "val": {
+            "uintVal": "0"
+          }
+        }
+      ]
+    }
+  }
+]

plugins/inputs/gnmi/testcases/issue_14530/telegraf.conf

@@ -0,0 +1,14 @@
+[[inputs.gnmi]]
+  addresses = ["dummy"]
+  encoding = "json_ietf"
+  tagexclude = ["path"]
+
+  [inputs.gnmi.tags]
+    test_tag = "test"
+
+  [[inputs.gnmi.subscription]]
+    name = "ifcounters"
+    origin = "openconfig"
+    path = "/interfaces/interface/state/counters"
+    subscription_mode = "sample"
+    sample_interval = "10s"