Implement \watch command

ksnnkyo · Apr 1, 2021 · 56dc9d5 · 56dc9d5
1 parent 35afc3a
commit 56dc9d5
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Showing 5 changed files with 46 additions and 3 deletions.
diff --git a/README.md b/README.md
@@ -564,13 +564,14 @@ Type "help" for help.
 
 (not connected)=> \?
 General
-  \q                              quit usql
   \copyright                      show usql usage and distribution terms
   \drivers                        display information about available database drivers
-  \g [FILE] or ;                  execute query (and send results to file or |pipe)
   \gexec                          execute query and execute each value of the result
+  \g [FILE] or ;                  execute query (and send results to file or |pipe)
   \gset [PREFIX]                  execute query and store results in usql variables
   \gx                             as \g, but forces expanded output mode
+  \q                              quit usql
+  \watch [SEC]                    execute query every SEC seconds
 
 Help
   \? [commands]                   show help on backslash commands

diff --git a/drivers/completer/completer.go b/drivers/completer/completer.go
@@ -192,6 +192,7 @@ func NewDefaultCompleter(r metadata.Reader) func(db metadata.DB) readline.AutoCo
 				`\timing`,
 				`\unset`,
 				`\w`,
+				`\watch`,
 				`\x`,
 				`\Z`,
 			},

diff --git a/handler/handler.go b/handler/handler.go
@@ -402,6 +402,8 @@ func (h *Handler) Execute(ctx context.Context, w io.Writer, res metacmd.Result,
 	}
 	f := h.execOnly
 	switch res.Exec {
+	case metacmd.ExecWatch:
+		f = h.execWatch
 	case metacmd.ExecSet:
 		f = h.execSet
 	case metacmd.ExecExec:
@@ -766,6 +768,34 @@ func (h *Handler) execOnly(ctx context.Context, w io.Writer, prefix, qstr string
 	return f(ctx, w, prefix, qstr, execParams)
 }
 
+// execWatch repeatedly executes a query against the database.
+func (h *Handler) execWatch(ctx context.Context, w io.Writer, prefix, qstr string, qtyp bool, execParams map[string]string) error {
+	sec := 2
+	if a, ok := execParams["interval"]; ok {
+		var err error
+		sec, err = strconv.Atoi(a)
+		if err != nil {
+			return text.ErrInvalidValue
+		}
+	}
+	for {
+		fmt.Fprintf(w, "%s (every %ds)\n", time.Now().Format(time.RFC1123), sec)
+		err := h.execOnly(ctx, w, prefix, qstr, qtyp, execParams)
+		if err != nil {
+			return err
+		}
+		watchCtx, cancel := context.WithTimeout(ctx, time.Duration(sec)*time.Second)
+		<-watchCtx.Done()
+		cancel()
+		if err := watchCtx.Err(); err != nil && !errors.Is(err, context.DeadlineExceeded) {
+			if errors.Is(err, context.Canceled) {
+				return nil
+			}
+			return err
+		}
+	}
+}
+
 // execSet executes a SQL query, setting all returned columns as variables.
 func (h *Handler) execSet(ctx context.Context, w io.Writer, prefix, qstr string, _ bool, execParams map[string]string) error {
 	// query

diff --git a/metacmd/cmds.go b/metacmd/cmds.go
@@ -172,6 +172,7 @@ func init() {
 				"gset":         "execute query and store results in " + text.CommandName + " variables,[PREFIX]",
 				"gx":           `as \g, but forces expanded output mode,`,
 				"crosstabview": "execute query and display results in crosstab,[COLUMNS]",
+				"watch":        "execute query every SEC seconds,[SEC]",
 			},
 			Process: func(p *Params) error {
 				p.Result.Exec = ExecOnly
@@ -210,6 +211,13 @@ func init() {
 							break
 						}
 					}
+				case "watch":
+					p.Result.Exec = ExecWatch
+					params, err := p.GetAll(true)
+					if err != nil {
+						return err
+					}
+					p.Result.ParseExecParams(params, "interval")
 				}
 				return nil
 			},

diff --git a/metacmd/types.go b/metacmd/types.go
@@ -92,6 +92,8 @@ const (
 	ExecExec
 	// ExecCrosstab indicates execution using crosstabview (\crosstabview).
 	ExecCrosstab
+	// ExecWatch indicates repeated execution with a fixed time interval.
+	ExecWatch
 )
 
 // Result is the result of metacmd execution.
@@ -102,7 +104,8 @@ type Result struct {
 	Exec ExecType
 	// ExecParams are accompanying parameters for execution. For ExecPipe, it
 	// will contain the key pipe with a filename and/or a command. For ExecSet
-	// it will contain the variable prefix.
+	// it will contain the variable prefix. For ExecWatch, it will contain
+	// the time interval value.
 	ExecParams map[string]string
 	// Crosstab are the crosstab column parameters.
 	Crosstab []string
-Original file line number
+Diff line change
@@ Expand Up @@
     				`\timing`,
     				`\unset`,
     				`\w`,
+    				`\watch`,
     				`\x`,
     				`\Z`,
     			},
@@ Expand Down @@