Add option to limit the number of rows in table

Sometimes, the table is rendered externally or with few outside parameters and
turns out to be too long to be displayed properly. It requires some slice
modifications in order to truncate the list and to introduce an ellipsis to
indicate that the table row count was reduced.

Add table option to tell the table renderer a limit on how many rows should be
added to the final result. An ellipsis is added to indicate that the number of
rows was truncated.

Author: HeavyWombat

go.sum

@@ -1,19 +1,10 @@
-github.com/DATA-DOG/go-sqlmock v1.3.3 h1:CWUqKXe0s8A2z6qCgkP4Kru7wC11YoAnoupUKFDnH08=
 github.com/DATA-DOG/go-sqlmock v1.3.3/go.mod h1:f/Ixk793poVmq4qj/V1dPUg2JEAKC73Q5eFN3EC/SaM=
 github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMoQvtojpjFo=
 github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
-github.com/gonvenience/bunt v1.0.6 h1:b3KEkaSlbXx3m4s2Gg5NfKkbo3YR3daCbqeecbDG9IE=
-github.com/gonvenience/bunt v1.0.6/go.mod h1:lsyhkmNpSAzhVx059BD0fQy5F29rWcS6AHb7UWNlT/s=
-github.com/gonvenience/bunt v1.0.7 h1:g4xg5OlNNNGNnwRZ/F4r3inRgnbfrbjnw1lO4BODmb4=
-github.com/gonvenience/bunt v1.0.7/go.mod h1:lsyhkmNpSAzhVx059BD0fQy5F29rWcS6AHb7UWNlT/s=
-github.com/gonvenience/bunt v1.1.0 h1:jKaW7wwtIS1pW29ykowAv1m5TdSo47uZgtZRGD4ss2c=
-github.com/gonvenience/bunt v1.1.0/go.mod h1:lsyhkmNpSAzhVx059BD0fQy5F29rWcS6AHb7UWNlT/s=
 github.com/gonvenience/bunt v1.1.1 h1:isYxOpDqbRMOSRhZtoux1tYvhhQ/AIbVDFrs24l6t0M=
 github.com/gonvenience/bunt v1.1.1/go.mod h1:lsyhkmNpSAzhVx059BD0fQy5F29rWcS6AHb7UWNlT/s=
 github.com/gonvenience/term v1.0.0 h1:joCB/j0Ngmdakd3muuLgAGPMf7DNKdoe708c1I6RiBs=
 github.com/gonvenience/term v1.0.0/go.mod h1:wohD4Iqso9Eol7qc2VnNhSFFhZxok5PvO7pZhdrAn4E=
-github.com/gonvenience/wrap v1.0.0 h1:N1zDI7z/uPd5ZQa8jII/ye/VENy3wgLXG962vw3ytMM=
-github.com/gonvenience/wrap v1.0.0/go.mod h1:L47Cm1sK1G8QmFAYQfkHcF/sQ1IBJUa0u4sjqiLqPdM=
 github.com/gonvenience/wrap v1.1.0 h1:d8gEZrXS/zg4BC1q0U4nHpPIh5k6muKpQ1+rQFBwpYc=
 github.com/gonvenience/wrap v1.1.0/go.mod h1:L47Cm1sK1G8QmFAYQfkHcF/sQ1IBJUa0u4sjqiLqPdM=
 github.com/hpcloud/tail v1.0.0 h1:nfCOvKYfkgYP8hkirhJocXT2+zOD8yUNjXaWfTlyFKI=
@@ -27,16 +18,10 @@ github.com/mattn/go-isatty v0.0.8/go.mod h1:Iq45c/XA43vh69/j3iqttzPXn0bhXyGjM0Hd
 github.com/mitchellh/go-ps v0.0.0-20170309133038-4fdf99ab2936 h1:kw1v0NlnN+GZcU8Ma8CLF2Zzgjfx95gs3/GN3vYAPpo=
 github.com/mitchellh/go-ps v0.0.0-20170309133038-4fdf99ab2936/go.mod h1:r1VsdOzOPt1ZSrGZWFoNhsAedKnEd6r9Np1+5blZCWk=
 github.com/onsi/ginkgo v1.6.0/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+WWjE=
-github.com/onsi/ginkgo v1.8.0 h1:VkHVNpR4iVnU8XQR6DBm8BqYjN7CRzw+xKUbVVbbW9w=
 github.com/onsi/ginkgo v1.8.0/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+WWjE=
-github.com/onsi/ginkgo v1.9.0 h1:SZjF721BByVj8QH636/8S2DnX4n0Re3SteMmw3N+tzc=
-github.com/onsi/ginkgo v1.9.0/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+WWjE=
 github.com/onsi/ginkgo v1.10.1 h1:q/mM8GF/n0shIN8SaAZ0V+jnLPzen6WIVZdiwrRlMlo=
 github.com/onsi/ginkgo v1.10.1/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+WWjE=
-github.com/onsi/gomega v1.5.0 h1:izbySO9zDPmjJ8rDjLvkA2zJHIo+HkYXHnf7eN7SSyo=
 github.com/onsi/gomega v1.5.0/go.mod h1:ex+gbHU/CVuBBDIJjb2X0qEXbFg53c61hWP/1CpauHY=
-github.com/onsi/gomega v1.6.0 h1:8XTW0fcJZEq9q+Upcyws4JSGua2MFysCL5xkaSgHc+M=
-github.com/onsi/gomega v1.6.0/go.mod h1:ex+gbHU/CVuBBDIJjb2X0qEXbFg53c61hWP/1CpauHY=
 github.com/onsi/gomega v1.7.0 h1:XPnZz8VVBHjVsy1vzJmRwIcSwiUO+JFfrv/xGiigmME=
 github.com/onsi/gomega v1.7.0/go.mod h1:ex+gbHU/CVuBBDIJjb2X0qEXbFg53c61hWP/1CpauHY=
 github.com/pkg/errors v0.8.1 h1:iURUrRGxPUNPdy5/HRSm+Yj6okJ6UtLINN0Q9M4+h3I=
@@ -55,7 +40,6 @@ golang.org/x/sys v0.0.0-20190412213103-97732733099d h1:+R4KGOnez64A81RvjARKc4UT5
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
-gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/fsnotify.v1 v1.4.7 h1:xOHLXZwVvI9hhs+cLKq5+I5onOuwQLhQwiu63xxlHs4=
 gopkg.in/fsnotify.v1 v1.4.7/go.mod h1:Tz8NjZHkW78fSQdbUxIjBTcgA1z1m8ZHf0WmKUhAMys=

table.go

@@ -47,6 +47,7 @@ type options struct {
 	columnAlignment   []Alignment
 	errors            []error
 	omitLinefeedAtEnd bool
+	rowLimit          int
 }
 
 func defaultOptions(cols int) options {
@@ -62,6 +63,7 @@ func defaultOptions(cols int) options {
 		columnAlignment:   alignments,
 		errors:            []error{},
 		omitLinefeedAtEnd: false,
+		rowLimit:          -1,
 	}
 }
 
@@ -119,6 +121,13 @@ func OmitLinefeedAtTableEnd() TableOption {
 	}
 }
 
+// LimitRows sets a limit at which point the table is truncated
+func LimitRows(limit int) TableOption {
+	return func(opts *options) {
+		opts.rowLimit = limit
+	}
+}
+
 // Table renders a string with a well spaced and aligned table output
 func Table(table [][]string, tableOptions ...TableOption) (string, error) {
 	maxs, err := lookupMaxLengthPerColumn(table)
@@ -138,11 +147,22 @@ func Table(table [][]string, tableOptions ...TableOption) (string, error) {
 	}
 
 	var (
-		buf     bytes.Buffer
-		lastIdx int = len(table) - 1
+		buf      bytes.Buffer
+		idx      int = 0
+		rowLimit int = len(table)
 	)
 
-	for i, row := range table {
+	if options.rowLimit >= 0 {
+		rowLimit = options.rowLimit
+	}
+
+	if rowLimit > len(table) {
+		return "", &RowLimitExceedsTableSize{Limit: rowLimit, Rows: len(table)}
+	}
+
+	for ; idx < rowLimit; idx++ {
+		row := table[idx]
+
 		if options.desiredRowWidth > 0 {
 			rawRowWidth := lookupPlainRowLength(row, maxs, options.separator)
 
@@ -190,7 +210,13 @@ func Table(table [][]string, tableOptions ...TableOption) (string, error) {
 		// Make sure to add a linefeed to the end of each line, unless it is
 		// the last line of the table and the settings indicate that there must
 		// be no linefeed at the last line
-		if lastline := i >= lastIdx; !lastline || !options.omitLinefeedAtEnd {
+		if lastline := idx >= rowLimit-1; !lastline || !options.omitLinefeedAtEnd {
+			// Special case in which the number of table rows is limited, add an
+			// ellipsis to indicate the truncation
+			if lastline && rowLimit >= 0 && rowLimit < len(table) {
+				buf.WriteString("\n[...]")
+			}
+
 			buf.WriteString("\n")
 		}
 	}

table_error.go

@@ -54,3 +54,14 @@ type ColumnIndexIsOutOfBoundsError struct {
 func (e *ColumnIndexIsOutOfBoundsError) Error() string {
 	return fmt.Sprintf("unable to render table, the provided column index %d is out of bounds", e.ColumnIdx)
 }
+
+// RowLimitExceedsTableSize is used to describe that the specified maximum row
+// number exceeds the actual number of rows in the table
+type RowLimitExceedsTableSize struct {
+	Limit int
+	Rows  int
+}
+
+func (e *RowLimitExceedsTableSize) Error() string {
+	return fmt.Sprintf("unable to render table, the provided row limit of %d exceeds the number of rows %d", e.Limit, e.Rows)
+}

table_test.go

@@ -168,5 +168,34 @@ un   deux trois`
 			Expect(err).ToNot(HaveOccurred())
 			Expect(tableString).To(BeEquivalentTo(expectedResult))
 		})
+
+		It("should be possible to limit the number of rows", func() {
+			input := [][]string{
+				{"eins", "zwei", "drei"},
+				{"one", "two", "three"},
+				{"un", "deux", "trois"},
+			}
+
+			expectedResult := `eins zwei drei
+one  two  three
+[...]
+`
+
+			tableString, err := Table(input, LimitRows(2))
+			Expect(err).ToNot(HaveOccurred())
+			Expect(tableString).To(BeEquivalentTo(expectedResult))
+		})
+
+		It("should fail when using an invalid row limit", func() {
+			input := [][]string{
+				{"eins", "zwei", "drei"},
+				{"one", "two", "three"},
+				{"un", "deux", "trois"},
+			}
+
+			tableString, err := Table(input, LimitRows(4))
+			Expect(err).Should(MatchError(&RowLimitExceedsTableSize{4, 3}))
+			Expect(tableString).To(BeEquivalentTo(""))
+		})
 	})
 })